This is the question........
A 20 kg block is originally at rest on a horizontal surface for which the coefficient of
friction is 0.6. If a horizontal force is applied such that it varies with time as shown. Determine
the speed of block in 10 sec.

You need the value of g to know when will the body start moving (3 seconds in this case)
Because for the body to move, F>= 0.6Mg i.e. F>=120. Hence the body starts moving after 3 secs.

@Rajath there are two ways of doing this. Actually both are different approaches having same meaning.
If you are familiar with basic integration you can try integrating the net force wrt time to get the change in momentum hence you can find the velocity.
Or you can first try to sketch the graph of net force versus time and find it's area b/w t=3 to t=10.(Both are same methods actually as integration is nothing but area bounded). The area gives you the change in momentum therefore you can calculate velocity.
But remember that we are not finding area under the graph in the question. We have to sketch our own graph of net force (Just the given graph pull it downwards by 120 )

if you do that properly the area comes out to be 480.
hence the velocity would be 480/20= 24 m/s.

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This is the question........ A 20 kg block is originally at rest on a horizontal surface for which the coefficient of friction is 0.6. If a horizontal force is applied such that it varies with time as shown. Determine the speed of block in 10 sec.

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is the answer 58.8 m/s ?

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noop.....

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Is the answer 49 m/s ? (assuming g=10 m/s^2)

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what's the need of g here????

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You need the value of g to know when will the body start moving (3 seconds in this case) Because for the body to move, F>= 0.6

Mg i.e. F>=120. Hence the body starts moving after 3 secs.Log in to reply

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Oh!! i got the question wrong!! the answer must be 24 m\s. (with g=10 m\s^2)

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yeah its right......how did u do it..................

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@Rajath there are two ways of doing this. Actually both are different approaches having same meaning. If you are familiar with basic integration you can try integrating the net force wrt time to get the change in momentum hence you can find the velocity. Or you can first try to sketch the graph of net force versus time and find it's area b/w t=3 to t=10.(Both are same methods actually as integration is nothing but area bounded). The area gives you the change in momentum therefore you can calculate velocity. But remember that we are not finding area under the graph in the question. We have to sketch our own graph of net force (Just the given graph pull it downwards by 120 )

if you do that properly the area comes out to be 480. hence the velocity would be 480/20= 24 m/s.

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Answer is 24 m/s

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