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June 2016 p42 q6
3443
A car of mass 1100 kg is moving on a road against a constant force of 1550 N resisting the motion.
(i) The car moves along a straight horizontal road at a constant speed of 40 m s-1.
Calculate, in kW, the power developed by the engine of the car. [2]
Given that this power is suddenly decreased by 22 kW, find the instantaneous deceleration of the car. [3]
(ii) The car now travels at constant speed up a straight road inclined at 8° to the horizontal, with the engine working at 80 kW. Assuming the resistance force remains the same, find this constant speed. [3]
Solution
(i) (a) The power developed by the engine is given by the formula:
\(P = Fv\)
where \(F = 1550 \text{ N}\) and \(v = 40 \text{ m s}^{-1}\).