Question

A car weighing 9800 N travels at 30 m/s. What braking force brings it to rest in 100m? In 10 m?

Answer 1

As per kinematics equation we know that

final speed of the car = 0 m/s

initial speed is given as 30 m/s

distance moved = 100 m

now we have

`v_f^2 - v_i^2 = 2 a d`

`0 - 30^2 = 2(a)(100)`

`a = - 4.5 m/s^2`

now braking force is given as

`F = ma`

now for mass we know that the weight of car is

`W = mg = 9800 N`

so mass of car is

`m = 1000 kg`

now we have

`F = 1000(4.5) = 4500 N`

Part b)

Again we have

final speed of the car = 0 m/s

initial speed is given as 30 m/s

distance moved = 10 m

now we have

`v_f^2 - v_i^2 = 2 a d`

`0 - 30^2 = 2(a)(10)`

`a = - 45 m/s^2`

now braking force is given as

`F = ma`

mass of car is

`m = 1000 kg`

now we have

`F = 1000(45) = 45000 N`