A mass m is hanging on a string that passes over a pulley and is then attached to another mass 3m that is resting on a horizontal table. Neglect friction. Mass m is held motionless and is then released. When it has fallen a distance h, it will have a speed v which can be calculated from the formula
E) None of these is correct.

Question

Quizplus · Accepted Answer

According to the conservation of energy, the potential energy lost by mass m is equal to the kinetic energy gained by mass 3m. 
mgh = 1/2 (3m)v^2 
Solving for v, we get v = sqrt(2gh/3). 
Substituting the given value of h, v = sqrt(2g(3L)/3) = sqrt(6gL)/sqrt(3) = sqrt(2gL). 
Therefore, the correct answer is B.

A Mass M Is Hanging on a String That Passes