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Certain force acting on a body of $20 kg$ changes its velocity from $5 m / s$ to $2 m / s$ . Calculate

the work done by the force.

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210 J

- 210 J

60 J

- 60 J

answer is B.

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Detailed Solution

The work done by the force is given by

210 J

.
Work is said to be done when a force, applied to an object, moves that object.
Kinetic energy is given by the expression,

(K . E)_{v} = \frac{1}{2} m v^{2}

Where

K . E =

Kinetic energy of the object

m =

mass of the object

v =

velocity of the object
When the object was moving at a speed of

5 m / s

, kinetic energy was present.

\Rightarrow (K . E)_{5} = \frac{1}{2} \times 20 \times (5)^{2}

\Rightarrow (K . E)_{5} = 250 J

When the object was moving at a speed of

2 m / s

, kinetic energy was present.

\Rightarrow (K . E)_{2} = \frac{1}{2} \times 20 \times (2)^{2}

\Rightarrow (K . E)_{2} = 40 J

Work done is responsible for the change in the kinetic energy of an object. It is also equal to
the change in kinetic energy if we are working with conservative forces only

Work done = Change in kinetic energy

= 40 J – 250 J

= - 210 J

Therefore,

work done = - 210 J

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