Answer to Question #130352 in Physics for Elvis

Question #130352

1.A ball of mass1kg is dropped from a height of 7m and rebounds to a height of 4.5m. Calculate: (a) its Kinetic Energy just before impact. (b) its initial rebound velocity and Kinetic Energy. Account for the loss of Kinetic Energy on impact.


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Expert's answer
2020-08-24T11:56:23-0400

(a) kinetic energy of a ball just before impact

KE1=mv22=mgh1=1kg×9.8N/kg×7m=68.6JKE_1=\frac{mv^2}{2}=mgh_1\\ =1\:\rm kg\times 9.8\: N/kg\times 7\: m=68.6\: J

(b) the initial rebound kinetic energy of a ball

KE2=mv222=mgh2=1kg×9.8N/kg×4.5m=44.1JKE_2=\frac{mv_2^2}{2}=mgh_2\\ =1\:\rm kg\times 9.8\: N/kg\times 4.5\: m=44.1\: J

the initial rebound velocity of a ball

v2=2gh2=2×9.8N/kg×4.5m=9.4m/sv_2=\sqrt{2gh_2}=\sqrt{2\times 9.8\:\rm N/kg\times 4.5\: m}=9.4\:\rm m/s

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