A motor car of mass 25 quintals is moving with a velocity of 36 km/hr. By the application of brakes it is brought to rest in a distance of 25 m. Find the average force of resistance.
Answers
Given info : A motor car of mass 25 quintals is moving with a velocity of 36 km/hr. By the application of brakes it is brought to rest in a distance of 25 m.
To find : the average force of resistance is ...
solution : mass of car, m = 25 quintals = 25 × 100 kg = 2500 kg [∵ 1 quintal = 100 kg ]
initial velocity of the car, u = 36 km/h = 36 × 5/18 m/s = 10 m/s [ ∵ 1 km/h = 5/18 m/s ]
final velocity of the car, v = 0 m/s
distance travelled by the car before stopping, s = 25 m
now using formula, v² = u² + 2as
⇒ 0² = 10² + 2 × a × 25
⇒ a = - 2 m/s²
now the force of resistance = mass of car × acceleration
= 2500 kg × - 2 m/s² = -5000N
here negative indicates that force is applied to stop the car.
therefore the average force of resistance is 5000N.