question_answer

A block of mass \[m=1\text{ }kg\]is moving with a constant acceleration \[a=1\text{ }m/{{s}^{2}}\]on a rough horizontal plane. The coefficient of friction between the block and plane is\[u=0.1\]. The initial velocity of block is zero at\[t=0\]. The power delivered by the external agent at a time t = 2 sec from the beginning is equal to \[\left( Takeg= 10m/{{s}^{2}} \right)\]

A) 1 watt  

B)        2 watt

C) 3 watt  

D)        4 watt

Correct Answer: D

Solution :

[d] \[\operatorname{m}= 1 kg, a = 1 m/{{s}^{2}}\] \[\mu =0.1\] \[f=\mu \,\,mg=0.1\times 1\times 10=1N\] \[{{\operatorname{F}}_{ext}}=ma+f~~~{{F}_{ext}}=1+l=2N\] \[\operatorname{v}=u +at=0+1\times 2=2m/sec.\] \[\therefore ~~P={{F}_{ext}}v=2\times 2=4watt.\]