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A trolley run...

Question

A trolley runs from point P to Q along a track, as shown in the figure. At point Q, its potential energy is 50 kJ less than at point P. At point P, the trolley has kinetic energy 5 kJ. Between P and Q, the work done against friction is 10 kJ. What is the kinetic energy at point Q?

A

35 kJ

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B

45 kJ

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C

55 kJ

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D

65 kJ

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Solution

The correct option is B 45 kJ
Let gravitational PE at Q be 0.
Use conservation of energy:
(GPE + KE) at Q + Work done against friction = (GPE + KE) at P
0 + KE at Q + 10k = 50k + 5k
So, KE at Q = 45 kJ

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