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Question
A ball of mass 0.5 kg slows down from a speed of 10 m s-1 to that of 6 m s-1. Calculate the change in the kinetic energy of the ball.
Solution
Mass of ball = 0.5 kg
Initial velocity = 10m s-1
Final velocity = 6 m s-1
∴ Initial K.E. = `1/2 mv^2`
= `1/2 xx 0.5 xx 10 xx 10`
= 25 J
Final K.E. = `1/2 mv^2`
= `1/2 xx 0.5 xx 6 xx 6`
= 9 J
Change in K.E. = 25 – 9 = 16 J
∴ K.E. decreases by 4 J
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