Need Science Help?

[Lixivium]

Let's say the two alleles of the gene are T (dominant) and t (recessive). Since the gene for tasting PTC is dominant, those people who can taste it are either TT or Tt, and those who can't are tt.

Tt + TT = 150
tt = 215 - 150 = 65

Percentage of people who are tt:
65/215 = 0.3

Percent frequency of each allele:
tt = q^2
q = sqrt(tt) = sqrt(0.3) = 0.55
P = 1 - 0.55 = 0.45

Frequencies of each genotype:
TT = P^2 = 0.45^2 = 0.2
tt = q^2 = 0.55^2 = 0.3
Tt = 2*P*q = (1 - TT - tt
= (1 - 0.2 - 0.3)
= 0.5

Multiply the frequencies by the population (215 people) to get the number of people:
TT = 0.2 * 215 = 43
tt = 0.3 * 215 = 65
Tt = 0.5 * 215 = 107
or
Tt = 215 - 43 - 65 = 107



I think that's how you do it. Not sure though, because it's been several years since I last did these problems.

 

[GoldShadow]

Everyone who has a dominant allele (the homozygous dominant, p^2, and the heterozygotes, 2pq) can taste PTC, or 150/215, which =.698. If p^2 + 2pq = .698, then q^2=1-.698, or 0.302.

Knowing that, you can do the rest of the problem:

q=sqrt(q^2)=sqrt(.302)=0.55

Then remember that p+q=1 to find p, and then you can find the remaining frequencies (p^2 and 2pq).

edit: Lixivium got to it first and did it right.

 

[Lixivium]

That's probably because of the body's natural cycles/rhythms. Blood pressure peaks sometime during mid-day/evening, around 3-6 pm. Then it starts to decrease later in the evening until morning again. Heart rate also peaks around the same time. Combined with the fact that you're probably more active during the day than when you just wake up (which also increases heart rate/blood pressure), that's why your blood vessels protrude more or less depending on time of day.

That might be true, but I think it's more likely that you're holding your arm in a posture that constricts certain veins, so that pressure is added to other veins and they bulge.

Also, when your arms are hanging down, you add the hydrostatic pressure of all the blood above your arm/hand to the veins in your arm/hand.

Next time you notice veins bulging in your arm/hand, raise your arm above your shoulder and they will more than likely disappear.

When you're lying down, your arm is generally relaxed, and of course you don't have the increase in hydrostatic pressure.

 

[Black Waltz]

I hope this thread is still alive...need some help with AP Chem.

Calculate the equilibrium partial pressure of PCl3 in a 3.00-L vessel that was charged with 0.123 atm of PCl5.
PCl5(g) <--> PCl3(g) + Cl2(g)

(Keq = 0.0121)

Help please?

 

[GoldShadow]

I hope this thread is still alive...need some help with AP Chem.

Calculate the equilibrium partial pressure of PCl3 in a 3.00-L vessel that was charged with 0.123 atm of PCl5.
PCl5(g) <--> PCl3(g) + Cl2(g)

(Keq = 0.0121)

Help please?

I'm pretty sure this works the same as any other equilibrium problem, except you use the partial pressures instead of concentrations. In other words:

(partial pressures of products)/(partial pressures of reactants)= Keq

So for this problem:

Keq=.0121 = (partial pressure PCl3)(partial pressure Cl2)/(partial pressure PCl5)

Set up the problem like so:

0.0121 = (x)(x)/(.123-x), where x is the partial pressure you're solving for. If you have any questions about how I got this or why I set it up like this, just ask and I'll clarify. Note that the volume of the container doesn't make any difference in this problem.

 

[Black Waltz]

Ahh, thanks Gold, you're a lifesaver. I actually get it now.

 

[Death]

I need some physics help (*coughGoldcough*)

Use Newton's Laws to explain why each of the following statements is correct. Which of the three laws best explains each one?

a) It takes longer for a car to accelerate from 0-100 km/h if it has five passsengers in it thaen when it has only one.



Increase in mass will cause longer acceleration time?

b) Many a novice hunter has experienced a sore shoulder after firing a shotgun.

Newton's Third Law? You push something, it will push back at you in opposite direction, equal magnitude?

c) Subway cars provide posts and overhead rails for standing passengers to hold.

????

According to Newton's Third Law, when a horse pull on a cart, the cart pulls back with an equal force on the horse. If, in fact, the cart pulls back on the horse as hard as the horse pulls forward on the cart, how is it possible for the horse to accelerate the cart?


A fully loaded Saturn V rocket had a mass of 2.92 x 10^6 kg. Its engines produced a thrust of 3.34 x 10^7 N.

a) What was the downward gravitational force acting on the rocket at life-off? (2.86 x 10^7 N)
b) What was the unbalanced force on the rocket at life-off? (4.8 x 10^6 N)
c) What was the acceleration of the rocket as it left the launch pad? (1.6 m/s^2)
d) As the rocket travelled upward, the engine thrust remained the same, but the mass of the rocket decreased. Why?
e) Did the acceleration of Saturn V increase, decrease of remain the same as the engines continued to fire?

A 20.0 kg toboggan is pulled along at a constant speed by a horizontal force of 30.0 N.

a) What is the gravitational force acting on the toboggan? (196 N)
b) What is the coefficient of friction? (0.153)
C) What force would be required to pull the toboggan with two 60.0 kg girls sitting on it? (2.10 x 10^2 N).

 

[M.K]

c) Subway cars provide posts and overhead rails for standing passengers to hold.

????

This is a combination of the first law and the third law.
The first law states that an object in motion will remain in motion unless acted upon by an unbalanced force. The force of the Subway car forces you to apply the "force" to a post and/or overhead rail in order to maintain balance, leading to the third law.
The third law states that for every action, there is an equal and opposite reaction. The act of you grabbing on to a post or overhead rail provides the opposite force required to maintain harmony between the Subway car's pull and the handle you use to help yourself stay balanced.

This could be totally wrong, I'm just a 10th grader with basica Physics knowledge from my Astronomy class.

GoldShadow, does this look right?

 

[zrky]

I need some physics help (*coughGoldcough*)

Use Newton's Laws to explain why each of the following statements is correct. Which of the three laws best explains each one?

a) It takes longer for a car to accelerate from 0-100 km/h if it has five passsengers in it thaen when it has only one.



Increase in mass will cause longer acceleration time?

b) Many a novice hunter has experienced a sore shoulder after firing a shotgun.

Newton's Third Law? You push something, it will push back at you in opposite direction, equal magnitude?

c) Subway cars provide posts and overhead rails for standing passengers to hold.

????

a) would be F=ma, the more mass the car has, the more acceleration it needs to get to the needed velocity.

b) yup, every force has an equal and opposite reaction
c) 1st law, an object at rest wil remain at rest unless acted upon by another force, basically your going as fast as the subway when your in it, so when it stops your going as fast as it was, therefore you need something to hold on to


According to Newton's Third Law, when a horse pull on a cart, the cart pulls back with an equal force on the horse. If, in fact, the cart pulls back on the horse as hard as the horse pulls forward on the cart, how is it possible for the horse to accelerate the cart?

The horse has traction, and because of the direction of the horse pulling the cart will 'push' in the same direction

A fully loaded Saturn V rocket had a mass of 2.92 x 10^6 kg. Its engines produced a thrust of 3.34 x 10^7 N.

a) What was the downward gravitational force acting on the rocket at life-off? (2.86 x 10^7 N)
b) What was the unbalanced force on the rocket at life-off? (4.8 x 10^6 N)
c) What was the acceleration of the rocket as it left the launch pad? (1.6 m/s^2)
d) As the rocket travelled upward, the engine thrust remained the same, but the mass of the rocket decreased. Why?
e) Did the acceleration of Saturn V increase, decrease of remain the same as the engines continued to fire?

A 20.0 kg toboggan is pulled along at a constant speed by a horizontal force of 30.0 N.

a) What is the gravitational force acting on the toboggan? (196 N)
b) What is the coefficient of friction? (0.153)
C) What force would be required to pull the toboggan with two 60.0 kg girls sitting on it? (2.10 x 10^2 N).

hope I helped and I lost you on the others

I have a question that I just CAN'T find in the book
1)Living things adjust to stimulus by reaction caled a(n)_______

2)Living things change during their lives through______

they are so simple I can't ge the answer, can someone help?

 

[M.K]

hope I helped and I lost you on the others

I have a question that I just CAN'T find in the book
1)Living things adjust to stimulus by reaction caled a(n)_______

2)Living things change during their lives through______

they are so simple I can't ge the answer, can someone help?

1) Response.

2) Development

 

[zrky]

OK, I hope it's right, il trust you, thanks.

 

[Lixivium]

A fully loaded Saturn V rocket had a mass of 2.92 x 10^6 kg. Its engines produced a thrust of 3.34 x 10^7 N.

a) What was the downward gravitational force acting on the rocket at life-off? (2.86 x 10^7 N)

This is easy. The "downward gravitational force" acting on an object is just its weight. I hope you know how to calculate the weight of an object if you already know its mass?

b) What was the unbalanced force on the rocket at life-off? (4.8 x 10^6 N)

This is a poorly-worded question but I assume it's asking what is the net force that is acting on the rocket? Well you have two forces acting on it: thrust from the engine and gravity. They are in opposite directions. I think you can figure this out.

c) What was the acceleration of the rocket as it left the launch pad? (1.6 m/s^2)

Force = Mass * Acceleration. Therefore Acceleration = Force / Mass. Easy.

d) As the rocket travelled upward, the engine thrust remained the same, but the mass of the rocket decreased. Why?

LOL WUT. That's just plain wrong. The mass of the rocket doesn't change at all. Relativistically speaking, it increases with velocity, but I don't think you guys are supposed to be discussing that.

The WEIGHT of the rocket will decrease because as you get further from the Earth, the force of gravity will decrease with the square of distance, so that the same amount of mass will "feel" less force acting on it.

e) Did the acceleration of Saturn V increase, decrease of remain the same as the engines continued to fire?

If the engines are putting out the same thrust, and the force of gravity decreases, then the net force will increase, and the acceleration will increase.

A 20.0 kg toboggan is pulled along at a constant speed by a horizontal force of 30.0 N.

a) What is the gravitational force acting on the toboggan? (196 N)

Again, this is just asking for the weight. I would hope you know how to do this.

b) What is the coefficient of friction? (0.153)

This is a little trickier. The force of friction is always opposite the direction of motion, and proportional to the gravitational force on an object.

Frictional force = k * m * g

where k is the coefficient of kinetic friction and m * g is the gravitational force (196 N).

I say "kinetic friction" because friction may be different when the object is not moving.

So then k = F / (m * g)

C) What force would be required to pull the toboggan with two 60.0 kg girls sitting on it? (2.10 x 10^2 N).[/I]

Now the weight is different, but the friction coefficient is still the same. Calculate the new gravitational force with your new mass (20 kg + 60 kg + 60 kg) and multiply by the frictional coefficient.

 

[Death]

Thats the thing. WE haven't learned how to calculate the weight of the object when mass is known???

 

[Lixivium]

Thats the thing. WE haven't learned how to calculate the weight of the object when mass is known???

Do you understand the concept of mass vs. weight? It's kind of important.

You can't do these problems if you don't even have that kind of basic understanding. Either you aren't paying attention in class or your teacher doesn't know what he/she is doing.

I suspect the former, but judging by the questions, I won't rule out the latter. If your teacher is bad, ask your parents/friends/other teachers for help now, because you're going to be in trouble later in the class.

 

[GoldShadow]

Regarding Death's physics Qs: zrky correctly answered all the ones he did, although I think Meta Kirby's reasoning here also sounds correct:

This is a combination of the first law and the third law.
The first law states that an object in motion will remain in motion unless acted upon by an unbalanced force. The force of the Subway car forces you to apply the "force" to a post and/or overhead rail in order to maintain balance, leading to the third law.
The third law states that for every action, there is an equal and opposite reaction. The act of you grabbing on to a post or overhead rail provides the opposite force required to maintain harmony between the Subway car's pull and the handle you use to help yourself stay balanced.

This could be totally wrong, I'm just a 10th grader with basica Physics knowledge from my Astronomy class.

GoldShadow, does this look right?

According to Newton's Third Law, when a horse pull on a cart, the cart pulls back with an equal force on the horse. If, in fact, the cart pulls back on the horse as hard as the horse pulls forward on the cart, how is it possible for the horse to accelerate the cart?

zrky's answer above is correct. It's because the equal and opposite forces act on different objects. This site explains it very well:
http://physicsstash.blogspot.com/2007/07/horse-and-cart-in-syllabus.html

Lixivium is right on the rest of them.

 

[Death]

Nope, you are wrong on both accounts Lixivium.

He is a good teacher and I do pay attention in class, it's just that these problems are due next week for me and I will not be in school at all. He also said he would teach use these concepts next week so I have to supplement what I won't learn directly in that class.

 

[aeolous]

Weight is just force applied by gravity, and any force is mass times acceleration. So, gravitational force (a.k.a. weight) is just the mass of the object times the acceleration of gravity (9.8 m/s^2).



And the mass of the rocket would decrease, because you are burning fuel and ejecting the products in order to propel the rocket, so the farther it gets, the longer the fuel has been burning, the less fuel the rocket is actually carrying, the less mass in the system.

 

[Lixivium]

And the mass of the rocket would decrease, because you are burning fuel and ejecting the products in order to propel the rocket, so the farther it gets, the longer the fuel has been burning, the less fuel the rocket is actually carrying, the less mass in the system.

I guess that's true. I've been in school too long to think outside the box like that.

 

[M.K]

Can anyone explain Demographic Transition to me? I was absent on the day that she gave us the defintion, and it's on a quiz that I take soon.

 

[Mr.Bazerkus]

in terms of meiosis

Why might their be 8 spores in the ascus instead of 4

 

[GoldShadow]

Partly because I'm bored and partly because I feel like it, I'm going to bring this thread back for the benefit of PRoomers and SWFers the world over.

Also I realize that these questions are like 1+ months old and Meta Kirby and Bazerkus probably don't need the answers anymore, but for the sake of completeness and kicking this thread up again, I'm going to answer them anyway.

Can anyone explain Demographic Transition to me? I was absent on the day that she gave us the defintion, and it's on a quiz that I take soon.

When a developing country becomes a developed country, there is a shift from high birth rates and high death rates (since in developing countries, people usually have more children and more people die earlier for a number of reasons) to lower birth rates and lower death rates (since in developed countries, people have fewer children and better health and sanitation means that they live longer). This usually means that the number of older people increases (since they live longer) and the number of young people decreases (since birth rates are lower) in developed countries. Wikipedia has a pretty good entry on it.
http://en.wikipedia.org/wiki/Demographic_transition

in terms of meiosis

Why might their be 8 spores in the ascus instead of 4

In an ascus, there may be a mitotic division after meiosis, doubling the number of spores from 4 to 8.

 

[SuperBowser]

Biology question, I guess.

Why do my blood vessels (ie...the back of my hand and arm) protrude more later in the day and do not after waking up?

Yeah, this is an oooold question, but I don't think blood pressure and heart rate have any effect on the size of cutaneous veins...

Your veins becoming prominent during the day is more likely to do with a combination of heat, exercise, gravity and sweating.

 

[GoldShadow]

Scientific American offers a good explanation for why veins appear to protrude during exercise:

Venous volume and pressure thereby decrease and are thus not the basis for the bulging. Instead, the process occurring in the capillaries as a result of the rise in arterial blood pressure during exercise causes plasma fluid otherwise resting in these tiny tributaries to be forced out through the thin vessel walls and into compartments surrounding the muscles. This process, known as filtration, causes a swelling and hardening of the muscle that is noticed during exercise. As a result of this swelling, cutaneous veins are pushed toward the skin surface, flatten to some extent, and appear to bulge. Such veins are more visible in persons with less subcutaneous fat. This bulging is neither good nor bad but simply a result of normal physiological mechanisms that result from the rise in arterial blood pressure during exertion.

(http://www.sciam.com/article.cfm?id=why-do-veins-pop-out-when)

I imagine similar reasoning applies to why they appear to protrude more at different times of the day; changes in body heat, heart rate, and blood pressure, which all more or less peak after mid-day and are pretty low during sleep and early morning.

 

[SuperBowser]

Hmm, interesting.

You shouldn't be using measured arterial blood pressures to prove vasodilation. The slight variations in our arterial blood pressure and heart rate during the day will have very little effect on venous pressure, if at all. For example, I've seen someone with a resting blood pressure of 200/140 but you would never know from looking at them.

It is just that when our heart rate and arterial blood pressure increase, we happen to be stressed or hot or exercising as well (and these things happen later in the day rather than when you wake up). Personally, my veins become very prominent whenever I use the underground trains (they're really hot..).

edit: even your source says blood pressure is not related to vasodilation

 

[GoldShadow]

I know what it says, I read it!

My source says that an increase in arterial blood pressure causes the surrounding muscle to swell, and that is what pushes cutaneous veins closer to the skin's surface (giving them the "popping" or "protruding" look).

 

[SuperBowser]

Ah. Well I misread you then. I figured since after establishing exercise as the root cause of vasodilation from your source, you wouldn't write heart rate and blood pressure separately again rather than exercise.

But I think that process only occurs in fairly intense exercise(?) rather than what the original poster was asking, which is most likely from body temperature.

 

[Death]

I have some physics test tomorrow and I was wondering about this question:

You throw a ball up into the air while travelling inside a moving car. To you, the ball goes up and comes down because it has the same velocity as the moving car. But why, to a pedestrian, does it look like the ball moves forward when you throw it into the air?

Also, are there any other examples that can be explained with Newton's Laws of Motion?

 

[GoldShadow]

While in a traveling car, everything in that car (including you, and the ball) has the same horizontal velocity as the car. So when a pedestrian (who is not moving) sees the ball, he sees it as moving forward at the same velocity as the car. To you in the car, however, it doesn't appear to be moving forward, because both you and the ball are moving with the same horizontal velocity (ie, you're moving forward at the same velocity as the ball).

 

[Azua]

I'm bumping this so the guy with the biology question can ask it here.

 

[ConnorTheKid]

thanks a lot Azua

 

[GoldShadow]

Copying your question from the other thread (though I'm not sure if you still need help with it):

I'm having a huge test tomorrow and I NEED to know the following things for the test:

the main differences between phenotypes and genotypes.

what a genotypic ratio and a phenotypic ratio is.

how Mendel's dihybrid crosses help him develop the law of independent assortment.

if you're working with 2 tall pea plants and know that one is Tt, how can you determine the genotype of the other plant?

I really need all the help I can get so any reply is appreciated

The genotype is their genetic makeup, which alleles they have. The phenotype is the the physical manifestation of it. Let's say there's a gene for hair color in horses "R". The dominant allele, R, codes red hair and the recessive allele, r, codes for white hair color. If the genotype is RR, the phenotype is red hair. If the genotype is Rr, the phenotype is red hair. If the genotype is rr, the hair is white.

The genotypic and phenotypic ratios are the ratios in a cross. So let's say we cross a male horse with genotype Rr with a female horse that has genotype Rr. This is what Punnett squares are for. The 4 resulting genotypes in the cross will be RR, Rr, Rr, and rr. So the genotypic ratio would be 1 RR:2 Rr:1 rr. The phenotypic ratio would be 3 red:1 white.

Mendel's dihybrid crosses were crosses in which he was observing two different traits (say, color and height). The allele for color has no effect on the allele for height. The genotypic/phenotypic ratios for color in a dihybrid cross are the same as if it were a monohybrid cross (see the horse example above); same with the ratios for height.

If you ever need to determine an unknown genotype, you perform a test cross; in other words, cross it with a plant that is homozygous recessive (in this case, tt); you can use the resulting phenotypic ratio to determine what the unknown was. For example, if you get all tall plants after the test cross, you know the unknown genotype is TT. If you get a ratio of 3 tall:1 short after the cross, you know the unknown genotype is Tt.

 

[rinoH]

GoldShadow prtty much summed it up are you in honors Connor

 

[Feocart]

Just a few quickies:

1) What is momentum?
2) How is momentum transfered?
3) What happens, in terms of momentum, when objects collide?

I want to get a little of a head start, seing as I haven't grasped it just yet..

 

[ConnorTheKid]

GoldShadow prtty much summed it up are you in honors Connor

yeah, I'm in honors.

thanks a lot GoldShadow!

 

[rinoH]

nice i am too

 

[ConnorTheKid]

2 more questions: why does the expected genotypic ratio often differ from the expected phenotypic ratio resulting from a monohybrid cross?

also, what would be the phenotypic ratios of the offspring resulting from the following cross: YYRr x YyRr?

 

[SuperBowser]

They differ because of the dominant allele. For example if T is dominant for being tall, you will always be tall if you are TT or Tt. However the genotype is different in both cases, as you can see.

In your second question, because the first subject is YY, you can infer that all offsrping will have the phenotype Y (since Y will always be part of the offsrping's genotype). Then you just have to work out the cross between the Rr and Rr using the method GoldShadow already showed.

 

[GoldShadow]

They differ because of the dominant allele. For example if T is dominant for being tall, you will always be tall if you are TT or Tt. However the genotype is different in both cases, as you can see.

In your second question, because the first subject is YY, you can infer that all offsrping will have the phenotype Y (since Y will always be part of the offsrping's genotype). Then you just have to work out the cross between the Rr and Rr using the method GoldShadow already showed.

SuperBowser's right on both counts.

If you're having trouble calculating ratios, use Punnett squares. You've surely learned them in class. If you're not sure how to do it for a dihybrid cross, check out this web site here:
http://www.dwm.ks.edu.tw/bio/activelearner/10/ch10c4.html

 

[GoldShadow]

Just a few quickies:
1) What is momentum?
2) How is momentum transfered?
3) What happens, in terms of momentum, when objects collide?

Not sure what kind of detail you're looking for, but:
1) In a strictly mathematical sense, momentum is mass x velocity (p=mv).
2) Momentum is transferred from one object/particle to another by a collision.
3) When objects collide, some momentum from one object is transferred to the other (and vice versa). How much momentum is transferred depends on whether it is an elastic collision, inelastic collision, or something in between.

 

[Feocart]

Not sure what kind of detail you're looking for, but:
1) In a strictly mathematical sense, momentum is mass x velocity (p=mv).
2) Momentum is transferred from one object/particle to another by a collision.
3) When objects collide, some momentum from one object is transferred to the other (and vice versa). How much momentum is transferred depends on whether it is an elastic collision, inelastic collision, or something in between.

2) and 3) seem alright. You are right for 1) in a mathematical sense, but I was looking for a descriptive sense. You don't have to worry, its simplist definition is "mass/inertia in motion".

Thanks for the help.