Question

Two masses m1=1.0kg and m2=3.0kg are connected by a massless string which passes over a frictionless pulley.The masses are initially 10m above the ground.
a)Find the velocity of the masses at the instant,the lighter mass moves up a distance of 5.0m
b)The string is suddenly cut at that instant, calculate the velocity with which the two masses hit the ground

Answer 1

potential energy of mass 1 at start = 1 g * 10
potential energy of mass 2 at start = 3 g * 10
sum = 40 g Joules
when mass 1 is at 15 meters, mass 2 is at 5 meters
now
PE1 = 1 *g * 15
PE2 = 3 * g * 5
sum = 30 g Joules
loss of PE = 10 g Joules
that is the kinetic energy
(1/2)*1 * v^2 +(1/2)*3 * v^2 = 10 g
2 v^2 = 10 * 9.81
v^2 = 49
v =7 meters/second
Your turn now