Question

The driver of a car slams on the brakes when he sees a tree blocking the road. The car slows uniformly with acceleration of -5.75 m/s^2 for 4.40 s, making straight skid marks 60.0 m long, all the way to the tree. With what speed does the car then strike the tree? m/s

Answer 1

Answer:

0.99 m/s

Explanation:

t = Time taken = 4.4 seconds

u = Initial velocity

v = Final velocity

s = Displacement = 60 m

a = Acceleration = -5.75 m/s²

$s=ut+\frac{1}{2}at^2\\\Rightarrow u=\frac{s-\frac{1}{2}at^2}{t}\\\Rightarrow u=\frac{60-\frac{1}{2}\times -5.75\times 4.4^2}{4.4}\\\Rightarrow u=26.29\ m/s$

$v=u+at\\\Rightarrow v=26.29+(-5.75)\times 4.4\\\Rightarrow v=0.99\ m/s$

The car hits the tree at 0.99 m/s