Q4.6 Work and kinetic energy II (S)
A truck pulling a trailer of mass 4000 kg accelerates steadily from rest to a speed of 72 kmh-1 in 40 s.- How far does the truck travel during the period of acceleration?
- Calculate the work done by the truck on the trailer over this distance and show that it is equal to the increase in kinetic energy of the trailer.
Solution
Reveal
Hide

Solution
From the magnitude of the acceleration, we can find the force applied to the trailer by the truck, and the distance travelled.
First calculate the acceleration: 72 kmh-1=72×1000/3600=20 ms-1. Thus, the acceleration is
a=20/40=0.5 ms-2
- The truck travels a distance
The magnitude of the (constant) force applied by the truck on the trailer is
F=ma=2000 Ntherefore the work done by this force over 400m is
W=2000×400=8×105 JThe final kinetic energy of the trailer is
Not entirely unexpected!