Question 4:
Certain force acting on a 20 kg mass changes its velocity from 5 m s−1 to 2 m s−1. Calculate the work done by the force.
Answer:
Kinetic energy is given by the expression,
Where,
Ek = Kinetic energy of the object moving with a velocity, v
m = Mass of the object
(i) Kinetic energy when the object was moving with a velocity 5 m s−1
(ii) Kinetic energy when the object was moving with a velocity 2 m s−1
Work done by force is equal to the change in kinetic energy.
Therefore, work done by force = (Ek)2 – (Ek)5
= 40 − 250 = −210 J
The negative sign indicates that the force is acting in the direction opposite to the motion of the object.
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