Question

A system containing a frictionless pulley is described in the diagram on the right (the 2.0 kg box is on the floor while the 3.0 kg box is 0.5m high) . If this system is released, what will be the momentum of:


A. the 2.0 kg box when the 3.0 kg box hits the floor?

b. the 3.0 kg when it hits the floor?

Answer 1

To start:

Potential energy of 3 kg box
up .5 = m g h = 3*9.81*.5
14.72 Joules

3 kg hit floor point:
Potential energy of 2 kg box now
= 2 * 9.81 * .5 = 9.81 Joules

SO
14.72 - 9.81 = 4.92 Joules is in the kinetic energy of the two moving blocks, m = 3+3=5 kg
(1/2)(5)v^2 = 5
v = sqrt 2 m/s

momentum of 2 kg = 2 sqrt 2
momentum of 3 kg = 3 sqrt 2