An advertisement shows a 1239 kg car slowly pulling at constant speed a large passenger airplane to demonstrate the power of its newly-designed 58.7-hp (horsepower) engine. During the pull, the car passed two landmarks spaced 23.0 meters apart in 15.3 seconds. The passenger plane being towed is a Boeing 707, with a total weight of 62.5 tons. Calculate the force that opposes the motion. Assume that the efficiency of the car is such that 20.9% of the engine power is available to propel the car forward.

Question

mrnood · Answer

(BTW it REALLY is time you guys in the US progressed to the metric system - everything is SOOO much easier with a consistent set of units) (BTW look at the MESS of units in this question meters, seconds, kg, tons and h.p. all in the same question)

Power of engine = 58.7 HP
Power available for pulling (effective power)  is 20.9% of this. ( I suggest you convert this power to kW here to avoid confusion with units later on...)

Car and plane move 23m in 15.3s (So calculate the speed in m/s)

Power = Force x Velocity

You know the effective Power, you know the velocity, so you can calculate the force.

Note - the weight of the plane and car is not required to solve this problem because the speed is constant - there is no acceleration - so all the power available is used to overcome the resistive force.