Calculate the work done by the brakes of a car of mass 1000kg when its

1.	Calculate the work done by the brakes of a car of mass 1000kg when its speed is reduced from 20 m/s to 10 m/s.
Answer» Mass of car = 1000 kg Initial velocity, u = 20 m/s Final velocity, v = 10 m/s Retardation = a Distance covered = s Using third equation of motion v² – u²= 2as as = -150 Work done, W = Fs F = ma W = mas as = -150 W = (1000)(150) = -150 kJ Negative sign shows that the brakes are acting on the opposite direction of motion.

Calculate the work done by the brakes of a car of mass 1000kg when its speed is reduced from 20 m/s to 10 m/s.

Answer»

Mass of car = 1000 kg

Initial velocity, u = 20 m/s

Final velocity, v = 10 m/s

Retardation = a

Distance covered = s

Using third equation of motion

v² – u²= 2as

as = -150

Work done,

W = Fs

F = ma

W = mas

as = -150

W = (1000)(150) = -150 kJ

Negative sign shows that the brakes are acting on the opposite direction of motion.