Question

Ke Min is driving along on a rainy night at 23m/s when he sees a tree branch lying across the road and slams on the brakes when the branch is 60.0m in front of him. Ifthe coefficient of kinetic friction between the car's locked tires and the road is 0.41, will the car stop before hitting the branch? The car has a mass of 2400 kg.

Answer 1

From Newton second Law :
-0.4*m*g=ma
-0.4*g=a if g = 10m/s^2 the a=-4 m/s^2

using :
v=vo+at assume v=0 if the car stop

0 = 23-4*t then t= 5.75 s

using :
s=vo*t+0.5*a*t^2 = 132.25-0.5*4*5.75*5.75=132.25-66.125 = 66.125 m..

So, the car does not stop...the car hit the branch..