# Velocity-time graph for a body of mass 10 kg is shown in figure.  Work-done on the body in first two seconds of the motion is : Option 1)  12000 J Option 2) −12000 J Option 3) −45000 J Option 4) −9300 J

As we discussed in

Net work done by all the forces give the change in kinetic energy -

- wherein

Initial velocity = 50 m/s

Final velocity = 0

Therefore

Therefore at any time t, velocity is

v = 50 - 5 t

at t = 0, v = 50 m/s

at t = 2s, v = 40 m/s

Therefore done in first 2 second will be change in kinetic energy

Therefore

W = - 4500 J

Option 1)

12000 J

This is an incorrect option.

Option 2)

−12000 J

This is an incorrect option.

Option 3)

−45000 J

This is the correct option.

Option 4)

−9300 J

This is an incorrect option.

N

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