Linear Dynamics Help: friction and horizontal force

[Solemony]

Homework Statement

I've been having some problems trying to do a few lab questions for my physics class, I'm not very good at it but I do try to make the best of it so anyone that's willing to help me give me any pointers would be awesome. I have two physics problem and I'm supposed to do them online and I've provided snapshots of them as well:

1. A three-picket fence of mass 422 grams is pulled by a constant force of 0.667 N on a rough surface as shown in the animation. Find the magnitude of the force of friction in Newtons.

2. A three-picket fence is pulled by a constant-force spring over a horizontal frictionless surface as shown in the animation. The mass of glider + fence is 563 grams and the hanging mass is 49.5 grams. Find the magnitude of the horizontal force exerted by the pulling hand in Newtons.

Homework Equations

For (1) I know the equation for force of friction =μN and N=mg but I'm not sure how to obtain "μ" based on the animation provided.

For (2) The net force on the hanging mass would be T-m2g=m2a and the hands that's pulling the glider and fence would be T=m1a, since the force that's pulling it is Tension.
So, the a=m2/(m1+m2)g, so once we found the acceleration we can plug in the "a" to F=m1a, to find the horizontal force?
I have attached the pictures in this thread for better visualization as well. The picture shown that the glider have already passed the photogate, thus it shows the the gate time on it.

 

[NascentOxygen]

1. A three-picket fence of mass 422 grams is pulled by a constant force of 0.667 N on a rough surface as shown in the animation. Find the magnitude of the force of friction in Newtons.

Hi Solemony. http://img96.imageshack.us/img96/5725/red5e5etimes5e5e45e5e25.gif

I think we are expected to be able to determine the body's acceleration, so we need some data from the animation. I guess we can't see it playing? So what are those 3 times listed?

 

[Solemony]

Hi Solemony. http://img96.imageshack.us/img96/5725/red5e5etimes5e5e45e5e25.gif

I think we are expected to be able to determine the body's acceleration, so we need some data from the animation. I guess we can't see it playing? So what are those 3 times listed?

The times listed are:
t0:0000
t1:.0915
t2:.1721

The fence starts at rest from 12cm from a photogate and each gap/picket is 2cm wide.

 

[NascentOxygen]

The times listed are:
t0:0000
t1:.0915
t2:.1721

The fence starts at rest from 12cm from a photogate and each gap/picket is 2cm wide.

Can you explain what useful information that data conveys?

 

[Nickie]

Hi! It's great that you're working on these physics problems and trying your best. Here are some tips that may help you with these questions:

1. For the first question, you are correct that the equation for force of friction is μN, where μ is the coefficient of friction and N is the normal force (which is equal to the weight, mg, in this case). The animation shows that the force of the hand is 0.667 N, so this is the applied force. To find the force of friction, you need to use the equation Ffr = μN. You can rearrange this equation to solve for μ: μ = Ffr/N. So, you just need to find the normal force and then plug in the values to solve for μ. The normal force can be found by considering the forces acting on the fence: the applied force of 0.667 N and the weight of the fence (mg). Since the fence is not moving vertically, the normal force must be equal and opposite to the weight, so N = mg. Once you have found μ, you can plug it back into the equation Ffr = μN to find the force of friction.

2. For the second question, you are correct that the net force on the hanging mass is T-m2g=m2a. However, the equation T=m1a is not quite right. The tension (T) is the force exerted by the spring, and it is equal to the force exerted by the hand (since the spring is attached to the hand). So, T is actually equal to the applied force in this case. To find the acceleration, you need to use the equation a = (T-m2g)/m1. Once you have found the acceleration, you can plug it into the equation F = m1a to find the horizontal force exerted by the hand.

I hope this helps! Remember to always carefully consider the forces acting on an object and use the appropriate equations to solve for unknown quantities. Keep practicing and don't be afraid to ask for help if you get stuck. Good luck with your physics class!