Physics Question pt. 4

Question

I'm really struggling with this problem. If anyone could help me out with this it would be greatly appreciated:

4.) A puck of mass m = 1.50 kg slides in a circle of radius r = 15.0 cm on a frictionless table while attached to a hanging cylinder of mass M = 2.80 kg by a cord through a hole in the table. What speed keeps the cylinder at rest?

Answer 1

This is centripetal motion.  We use the formula

 

F_c = mv² / r

 

where:

m = mass

v = velocity

r = radius

 

The centripetal force of the puck will the same as the centripetal force of cylinder due to Newton's 3rd law.

 

Fc _puck = Fc _cylinder

 

Since the cylinder will be at rest, the velocity of the cylinder is v=0. Therefore, we have

 

(1.5v² / 15) = 0

 

Solving for v of the puck will yield a velocity of zero.