Force of friciton always act opposite to direction of motion of object So it is negative force


When a ball is thrown with a force, it is postive work (as ball moves in direction of force applied)

However, ball stops after some time (it is negative work as ball moves opposite to direction of force applied)

It is because of the negative work(force is in the direction opposite to motion) done by the friction on the ball.

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Davneet Singh
Davneet Singh is a graduate from Indian Institute of Technology, Kanpur. He has been teaching from the past 9 years. He provides courses for Maths and Science at Teachoo.