Two blocks of masses m1=4kg and m2=5kg are connected by a massless string that passes over a massless frictionless pulley.block m1 is initial at rest on asmooth horizontal plane while block m2 is at a height h =0.75m above the ground.find the speed of the masses just before m2 hits the ground.

Answer 1

the external force on the system is gravity on m1

F = m1 * g

the acceleration of the system is F divided by the system mass (M)

a = F / M = (m1 * g) / (m1 + m2) = .444 g

kinetic energy = work done by gravity ... 1/2 M v^2 = m1 * a * h

v = √[2 * 4 * .444 g * 0.75 / (4 + 5)] ... m/s