Question

A 4 kg block resting on a frictionless horizontal ledge is attached to a string that passes over a pulley and is attached to a hanging 2 kg block. The pulley is a uniform disk of radius 13.0 cm and mass 0.50 kg.

(a) Find the speed of the 2 kg block after it falls from rest a distance of 2.5 m.

(b) If an additional 5.0 mJ of energy are supplied to the rotational energy, what is the new angular speed of the ball?

Answer 1

look at the energy change:

change in PE=change in KE
2*g*2.5=1/2 (4+2)v^2 + 1/2 I w^2

where I is the moment of inertia for a pulley ( I would model it as a solid disk)
now to relate w to v, remember w=v/r

b) makes no sense to me.