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? (in kJ)

Answer 1

Let potential energy at P = PP and let potential energy at Q = PQ.

From the question, PP – PQ = 50kJ

Let kinetic energy at Q = KQ

So from conservation of energy,

Sum of energies at P = Sum of energies at Q + Work against friction

PP + KP = PQ + KQ + 10

PP + 5 = (PQ + KQ) + 10

KQ = (Pp – PQ) + 5 – 10 = 50 + 5 – 10 = 45kJ