Question

Find the magnitude of the net force required to stop a car with a mass of 1050 kg, initial speed is 40.0 km/h, and stopping distance 25.0 m.

Answer 1

1 km = 1000 m

1 hour = 3600 sec

Mass of the car = m = 1050 kg

Initial speed of the car = V₁ = 40 km/hr = 40 x (1000/3600) m/s = 11.111 m/s

Final speed of the car = V₂ = 0 m/s

Stopping distance = D = 25 m

Acceleration of the car = a

V₂² = V₁² + 2aD

(0)² = (11.111)² + 2a(25)

a = -2.469 m/s²

Negative as it is deceleration.

Net force = F

F = ma

F = (1050)(-2.469)

F = -2592.5 N

We are asked for the magnitude of the force therefore it will be positive.

Magnitude of the net force required to stop the car = 2592.5 N