Question

A car with a mass of 1200 kg is travelling at a constant speed of 20 m/s on a straight road. Suddenly the driver applies the brakes and the car comes to a stop in 5 seconds. Assuming the braking force is constant calculate the magnitude of the braking force acting on the car?

Answer 1

Answer: 4800 newtons

===============================================

Step-by-step explanation

Given info:

• vi = 20 = initial velocity
• vf = 0 = final velocity (since we want the car to stop)
• t = time duration = 5 seconds

Let's calculate the acceleration.

a = (vf - vi)/t

a = (0-20)/5

a = -4

The acceleration of the car is -4 m/s^2. The negative acceleration (aka deceleration) means the braking force acts opposite the car's direction. This is of course to slow the car down.

Each second, the car's speed slows down by 4 m/s.

Now we'll use Newton's second law to determine the braking force.

force = mass*acceleration

F = ma

F = 1200*(-4)

F = -4800

The force is -4800 newtons. A negative force pushes against the car's direction to slow it down. I have a feeling your teacher only cares about the magnitude of this braking force, so the answer would be 4800 newtons