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Question

A block of ice mass 2.0 kg is pushed down an inclined plane of inclination 37 with a force of 20 N acting parallel to the incline. It is found that the block moves on the incline with an acceleration of 10m/s2 If the block started from rest, find the work done(Wf) by the applied force in the first second, Wg by the weight of the block in the first second and (Wf) by the frictional force acting on the block in the first second. Take g=10m/s2


A

WF =100 J; Wg = 60 J; Wf = 60 J

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B

WF =100 J; Wg = 60 J; Wf = -60 J

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C

WF =100 J; Wg = 100 J; Wf = 0 J

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D

None of these

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Solution

The correct option is B

WF =100 J; Wg = 60 J; Wf = -60 J


So question is asking for work done in the first second

a=10ms2

u=0ms

t=1sec

So, in 1 sec displacement of block will be s=ut+12at2

s = 5m

WF = Work done by force = F×s×cosθ

= 20×5×cos0

= 100 J

Wg = Work done by weight = mg×s×cosθ

=2×g×5×cos53

= 60 J

Wf = Work done by friction = fr×s×cosθ

Oh, so we need NLM to find friction from free body drawing of object.

F+mgcos53fr = ma

20+12fr=2×10

fr=12N

=Wf=12×5×cos180=60J


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