Question

At the end of a race, a runner decelerates from a velocity of 9 m/s at a rate of 2m/s^-2.
(a) How far does he travel in the next 5s? b) What is his final velocity?
(c) How much time will it take to finally stop?​

Answer 1

Answer:

(a) u=9m/s, a=-2m/s^-2,t=5s

By applying Newton's 3rd law of motion

s=ut+1/2at^2

s=9×5+1/2×(-2×5×5)

s=45-25

s=20m

(b) By applying Newton's 2nd law of motion

v^2=u^2+2as

v^2=9^2+2×(-2×20)

v^2=81-80

v^2=1

v=1m/s

(c) By applying Newton's 1st law of motion

v=u+at

1=9-2×t

2t=9-1

2t=8

t=4s