A 1kg ball is released and slides down from point A to point C, as shown in the figure below. If the acceleration due to gravity=10m/s2, the kinetic energy of the ball when it arrives at point C.
A
5.5J
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B
6.5J
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C
7.5J
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D
8.5J
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Solution
The correct option is C7.5J Taking ground as reference, Total mechanical energy of the ball at point A=UA+KEA=mghA+0 =(1)×(10)×2+0 =20J And, total mechanical energy of ball when it reaches point C =UC+KEC=mghC+KEC =KEC+(1×10×1.25) =KEC+12.5
From the principal of mechanical energy conservation, total energy of ball at point A equals the total energy of the ball at point C. ⟹(UA+KEA)=(UC+KEC) ⟹20=KEC+12.5 ⟹KEC=(20−12.5)=7.5J Hence , the kinetic energy of the ball when it reach at point C is 7.5J