KE and force?

Question

Hi. I have THREE questions. I tried them myself, but I'm confused. Please help!

1. If the force of friction on the crate is a steady 70 N, and it is pushed along a 10 m factory floor, how much KE is gained by the crate? (Is the answer 3500 MJ?)

2. A force of 50 N is applied to the end of a lever which is moved a certain distance. If the other end of the lever moves one third as far, how much force can it exert? (I don't even know how to start this one)

3. Consider an ideal pulley system. If you pull one end of the rope down with 50 N a distance of 1 meter, how high will you lift a 200 N load? (I don't know what to do here either!)

Please explain/give examples if necessary. The answers don't have to be long, but enough to understand the concepts. :)

Thank You!

Answer 1

I know what you mean...

1. I'm clueless since I do not know the force that did moving, however the work agains friction is
W=F s= 70 x 10=700 J

2. Sum of moment on the left is equal to the sum of moments on the right or

Ml=Mr M=r x F (vector product)

Based on similar triangles

r1 x F1= r2 F2 where 1/3r1=r2 we have

r1 F1=1/3 r1F2

F2= 3F1=150N

3. If it is a single pulley then it is 1:1 meaning you will not even budge th e200 N load with 50 N pull. So what is teh ratio or advantage? Say advantage is 5:1 then 1m of pull will lift the 200N load 1/5= 20cm.

Have fun