SELECT * FROM question_mgmt as q WHERE id=4204 AND status=1 SELECT id,question_no,question,chapter FROM question_mgmt as q WHERE courseId=8 AND subId=16 AND chapterId=191 and ex_no='5' AND status=1 ORDER BY CAST(question_no AS UNSIGNED) CBSE Free NCERT Solution of 9th science Work and Energy certain force acting on a 20 kg mass changes its v

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.

Answer:

Mass of the body = 20 kg

Initial velocity, u = 5 m/s

Final velocity, v = 2 m/s

Kinetic energy is given by the expression,

(i) Kinetic energy when the object was moving with a velocity 5 m/s

(ii) Kinetic energy when the object was moving with a velocity 2 m/s

Work done = change in kinetic energy. 

Therefore, work done = (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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