# Friction force homework problems

• gavrir
In summary: So in summary, the force sensor measures the force on the sensor due to the bumper, while the cart's momentum change arises from the force on the cart due to the bumper. To assert that these two forces are nearly equal at all times, we need to consider the force of friction being small and the cart's weight being canceled by the normal force exerted by the track.
gavrir
Hey guys this is a practice problem for my lab and i can't get it can someone please help:
The force sensor measures the force on the sensor due to the bumper, but the cart's momentum change arises from the force on the cart due to the bumper. Which of the following facts are needed to assert that the magnitude of these two forces are nearly equal at all times.

A. Their magnitudes differ by the magnitude of the net force on the bumper.

B. The force of friction is small.

C. The net force on the bumper is small.

D. The cart's weight is canceled by the the normal force exerted by the track.

1. A, B

2. A, C

3. A, D

4. B, C

5. B, D

6. C, D

7. A, B, C, D

Thanks!

gavrir said:
Hey guys this is a practice problem for my lab and i can't get it can someone please help:
The force sensor measures the force on the sensor due to the bumper, but the cart's momentum change arises from the force on the cart due to the bumper. Which of the following facts are needed to assert that the magnitude of these two forces are nearly equal at all times.

A. Their magnitudes differ by the magnitude of the net force on the bumper.

B. The force of friction is small.

C. The net force on the bumper is small.

D. The cart's weight is canceled by the the normal force exerted by the track.

1. A, B

2. A, C

3. A, D

4. B, C

5. B, D

6. C, D

7. A, B, C, D

Thanks!

can you describe a bit the physical situation? Where is the sensor, what is happening? It's a colision? The bumper is on what? It's hard to reply without some idea of the setup.

Well I have not done the lab yet, and these are practice pre-lab questions. But usually the force sensor is attactched to the end of the cart which is on a "frictionless" surface. It is an impulse and momentum lab and i believe that the bumber is on the end of the meterstick.

gavrir said:
Well I have not done the lab yet, and these are practice pre-lab questions. But usually the force sensor is attactched to the end of the cart which is on a "frictionless" surface. It is an impulse and momentum lab and i believe that the bumber is on the end of the meterstick.

Ok.

Basically, the change of momentum is due to the net force on the cart. While the sensor is measuring only the force on the cart due to the bumper. The question is then: why are these two forces nearly equal?
Another way of saying this is: why can you ignore all the other forces on the cart, beside the force exerted by the bumper?

Hint: what are the forces on the cart during the collision? Why can you ignore all the other forces beside the bumper force?

so then it is
A. Their magnitudes differ by the magnitude of the net force on the bumper.

B. The force of friction is small.

A and B correct?

actually the answer is all of them isn't it?

gavrir said:
actually the answer is all of them isn't it?

I would not agree... Two of them sounds right to me.

is it b and c?

gavrir said:
is it b and c?

What are the forces acting on the cart during the collision?

well the surface is considered frictionless but that's impossible right? there has to be some friction and the other is the applied force right?

gavrir said:
well the surface is considered frictionless but that's impossible right? there has to be some friction and the other is the applied force right?

Force applied by what? You are also forgetting the forces along y

o0oh the normal force and the force due to gravity, but since the motion is horizontal i thought those didnt matter...so I am guessing the answer is b and d which are friction and normal/gravity

gavrir said:
o0oh the normal force and the force due to gravity, but since the motion is horizontal i thought those didnt matter...so I am guessing the answer is b and d which are friction and normal/gravity

So during the collison, there is the force due to the bumper, a little bit of friction, the normal and the weight.

The question is : why can't we forget about the normal, the weight and the friction is say that the net force is basically just due to the force of the bumper?

there is no reason to say that the force of the bumper is much larger than the weight of the normal but we can forget about those because they cancel out.

And we can forget about the friction force because it must be much smaller than the bumper's force.

Choice A says that teh magnitude of the bumper's force and the net force differ by the net force on the bumper. This does not make sense. And there is nothing that say sthat the bumper force is small.

So here you go...

ok i think i got it now C and D?

gavrir said:
ok i think i got it now C and D?

Why do you have to assume that the force due to the bumper is small? If it was, we could not neglect friction compared to it.

sorry wrong choices i meant B and D

## Question 1: What is friction force?

Friction force is the force that resists the motion of an object when in contact with another object. It is caused by the microscopic irregularities on the surfaces of the objects and is dependent on the type of materials and the force pressing them together.

## Question 2: How is friction force calculated?

Friction force can be calculated by multiplying the coefficient of friction, which is a value that represents the roughness of the surfaces, by the normal force, which is the force that presses the objects together.

## Question 3: What factors affect the amount of friction force?

The amount of friction force is affected by the type of materials in contact, the roughness of their surfaces, the force pressing them together, and the speed of motion.

## Question 4: How does friction force impact motion?

Friction force can either slow down or stop the motion of an object. It also causes heat and wears down the surfaces of the objects in contact.

## Question 5: Can friction force be reduced?

Friction force can be reduced by using lubricants, which create a layer between the surfaces, or by using smoother materials. It can also be reduced by decreasing the force pressing the objects together.

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