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CBSE Class 9 Answered

During a football match, the ball shot towards the goal struck the defender's foot at the speed of 10m/s and it bounced back at 20m/s. if the time of impact was 0.2 sec, and mass of the ball 1/2 kg, then the average force exerted by defender on the ball???
Asked by SYOHAN | 26 Jul, 2012, 05:20: PM
answered-by-expert Expert Answer
Let us assume that the ball bounced back in the direction exactly opposite to what it had came.
mass of ball, m= 0.5 kg
Intial momentum: p1 = 0.5 x 10 = 5 kgm/s
final momentum: p2 = 0.5 x (-20) = 10 kgm/s (negative sign due to opposite direction of motion)
Thus change in momentum, p = p2-p1 = -15 kgm/s
Rate of change of momentum, t = 0.2 s
Thus force exerted on ball = p/t = -75 N
Answered by | 26 Jul, 2012, 10:44: PM

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