A car is travelling at 120 km/hr when it slams on the brakes...

Question

A car is travelling at 120 km/hr when it slams on the brakes.
a. How long is the skid mark if the coefficient of friction is 0.62? (hint: convert km/hr to m/s)

b. Explain why a more massive car does not take longer to stop, given that Newton’s 2nd Law tells us that a bigger force is required to slow down a bigger mass. Hint: mass also impacts ______________. Explain:

Answer 1

vo = 120/3.6 = 33.33 m/s

net force = Ff =(mu)N =(mu)mg = -ma

a=(mu)g = (0.62)(9.8) = -6.076 m/s/s

v^2 =vo^2 + 2ax

0 = 33.33^2 +2(-6.076)x

x = 91.41 m

b) since the deceleration a = (mu)g, it is independent of the mass of the car. So for a massive or light car we end up with the same deceleration so it will be the same stoping distance.