# A block of metal wheighing 2 kg is resting on a frictionless surface,if struck by a jet releasing water at the rate of 1kg/s and at a speed of 5m/s.what is the initial acceleration of the block ?

Jan 24, 2017

The final velocity of mass of water after hitting the metal block is zero.

So the average change in momentum per sec = initial momentum
$= \text{mass"xx"initial velocity of water}$

$= 1 k g \times 5 m \text{/s"=5kgm"/s}$

As this change in momentum occurs during 1 sec. We may say that the force exerted on the 2kg metal block is
$F = \text{change in momentum"/"time}$
$= \frac{5 k g m \text{/s}}{1 s} = 5 N$

Hence by Newton's law initial acceleration of the block of mass $m = 2 k g$ is given by

$a = \frac{F}{m} = \frac{5 N}{2 k g} = 2.5 m \text{/} {s}^{2}$