# Friction and pulley

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#1
This question has been troublesome, can anyone give me a bit of help please, I'd appreciate it.
0
1 month ago
#2
The first part of this answer uses the F=ma equation. You need to form one for each particle.

so for A, there is Friction acting in the opposite direction to movement and there is Tension in the direction of movement. You can calculate the friction because you have the coefficient and F = uR..
So the equation for A would be in the form,

T-uR = ma
You know the mass, and can calculate uR — you're trying to work out acceleration... let's leave this here and do the same for B.

Particle B has the Tension acting in the opposite direction to movement and has it's weight acting downwards (in the direction of movement).

The equation will take the form.
mg - T = ma
You can calculate mg because and know the mass.

Now look at these two particles. They are connected by the same string over a SMOOTH pulley. This means that the Tension is THE SAME. So to get rid of one of the unknowns in our two equations, we rearrange them for T, and then make simultaneous equations (basically set the two equal to each other after rearranging).

Now we have everything in terms of a — the acceleration. Solve for a and you should get your acceleration!!

The second part is finding the speed of B as it hits the ground, this is the easy bit!!
B will be, a falling particle but just without gravity acting as the acceleration.
So... use SUVAT!
We know that the string is 2.8m long, and 2.1m is before the pulley so B is hanging 0.7m below the pulley. So the distance it needs to fall is 2m - 0.7m which is 1.3m! And the particle starts at rest so U = 0 and the acceleration is the one you calculated earlier Remember you want to find V.

Put these values into the appropriate suvat equation, and you should find that you get the answer you are looking for...

I hope this helps <3
1
#3
(Original post by mxxnal)
The first part of this answer uses the F=ma equation. You need to form one for each particle.

so for A, there is Friction acting in the opposite direction to movement and there is Tension in the direction of movement. You can calculate the friction because you have the coefficient and F = uR..
So the equation for A would be in the form,

T-uR = ma
You know the mass, and can calculate uR — you're trying to work out acceleration... let's leave this here and do the same for B.

Particle B has the Tension acting in the opposite direction to movement and has it's weight acting downwards (in the direction of movement).

The equation will take the form.
mg - T = ma
You can calculate mg because and know the mass.

Now look at these two particles. They are connected by the same string over a SMOOTH pulley. This means that the Tension is THE SAME. So to get rid of one of the unknowns in our two equations, we rearrange them for T, and then make simultaneous equations (basically set the two equal to each other after rearranging).

Now we have everything in terms of a — the acceleration. Solve for a and you should get your acceleration!!

The second part is finding the speed of B as it hits the ground, this is the easy bit!!
B will be, a falling particle but just without gravity acting as the acceleration.
So... use SUVAT!
We know that the string is 2.8m long, and 2.1m is before the pulley so B is hanging 0.7m below the pulley. So the distance it needs to fall is 2m - 0.7m which is 1.3m! And the particle starts at rest so U = 0 and the acceleration is the one you calculated earlier Remember you want to find V.

Put these values into the appropriate suvat equation, and you should find that you get the answer you are looking for...

I hope this helps <3
Woah that was really helpful actually, I was not expecting this.
Thank you very much.
0
1 month ago
#4
(Original post by Mlopez14)
Woah that was really helpful actually, I was not expecting this.
Thank you very much.
Ite no problem! I know it's frustrating trying to do maths without any actual help — I made the regretful decision to take the whole Maths A-Level in one year and I didn't get a lot of help and it was hell ngl.
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