question_answer

A block of weight 4kg is resting on a smooth horizontal plane. If it is struck by a jet of water at the rate of 2kg/s and at the speed of 10 m/s, then the initial acceleration of the block is:

A) \[15m/{{s}^{2}}~\]                

B) \[10m/{{s}^{2}}\]

C) \[2.5m/{{s}^{2~}}\]               

D) \[5m/{{s}^{2}}\]

Correct Answer: D

Solution :

[d]  \[{{F}_{ext}}=\frac{d}{dt}(mv)\] \[{{F}_{ext}}=V\frac{dm}{dt}\] \[ma=V\frac{dm}{dt}\] \[4a=10\times 2\] \[a=5m/s\]