Question

Which of the following statements about this experiment is FALSE? Before each trial one should reshape the bob into something like a ball. You may assume the collision between the bob and the box is completely inelastic. The initial position for the box should be just touching the pendulum bob when it is hanging straight down. To make the box move, the pendulum bob should hit close to the bottom of the box during the collision

Answer 1

Which of the following statements about this experiment is FALSE? Before each trial one should reshape the bob into something like a ball. You may assume the collision between the bob and the box is completely inelastic. The initial position for the box should be just touching the pendulum bob when it is hanging straight down. To make the box move, the pendulum bob should hit close to the bottom of the box during the collision is given below

Explanation:

So, The bob is held at angle theta from initial position, P. Find the displacement from P.  

displacement= L sin  Θ. I hope you get it here. The pendulum forms a triangle with length L, the initial position and horizontal displacement.

So,the point is at displacement point the kinetic energy of bob is 0 and when it is released it will have maximum kinetic energy at P. It will hit the box and all he kinetic energy of bob will get transferred into driving force(F.D) of box. Now kinetic energy = Force * displacement.

K.E= 0.5 m V^2= F.D * Lsin Θ.

Find F.D

F.D = (0.5 m V^2) /  Lsin Θ.

Now for the box, F.D - Friction = m(box) a.

Friction = F.D + m(box) a.

Find the accelaration of box from an equation of motion. ( u=0, find displacement of box,s,time taken and so on)

U get the friction. Now,

coeff of friction = µ = friction/ reaction.

Note that reaction here = weight of box= m(box) g.   g= acc of free fall= 9.81.

So here u go.. U get the coeff of friction.. I hope am right here.. and made no mistake.. Anyway try it with the values to confirm! ;)