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# 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. - CBSE Class 9 - Science

ConceptWork and Energy Kinetic Energy

#### Question

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.

#### Solution

Kinetic energy is given by the expression,

(E_k)_v=1/2"mv"^2

Where,

E= 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

(E_k)_5=1/2xx20xx(5)^2=250J

Kinetic energy when the object was moving with a velocity 2 m s−1

(E_k)_2=1/2xx20xx(2)^2=40J

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.

Is there an error in this question or solution?

#### APPEARS IN

NCERT Solution for Science Textbook for Class 9 (2018 to Current)
Chapter 11: Work and Energy
Q: 4 | Page no. 158

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Solution 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. Concept: Work and Energy - Kinetic Energy.
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