Question

A block of metal weighing 2kg is resting on a frictionless plane. It is struck by a jet releasing water at the rate of 1kg/s and at a speed of 5m/s. Find the initial acceleration of the block.

Answer 1

You will have to make an assumption about what happens to the jet stream momentum as it splashes backwards. Since they don't tell you what to do, assume it loses all its momentum. The force on the block is then the mass flow rate times the incident velocity, or

F = 5 Newtons.

Use F = m a for the acceleration, a.

Answer 2

Jet releases water at the rate of 1 kg/sec
velocity = 5 m/s
Therefore force acting on the block = 1 x 5 = 5 N
acceleration = a = Force/Mass = 5/2 = 2.5 m/s2