Question

A car moving on a straight
highway with a speed of 72km/hr is
brought to a stop with in a distance of
100m.
(a) What is the retardation of the car?
(b) How long will it take for the cart
stop?​

Answer 1

Explanation:

First get your units standardised, so:

1h = 60 minutes of 60s each so 60x60=3600s

72km/h or 72000m/3600s = 20m/s

When the car slows it starts at 20m/s and finishes a 0m/s so the average speed over the 100m is 10m/s and if you’re travelling 10m each second, 100m will take 10s

The car is decelerating from 20m/s to 0 over 10s so each second it must loose (on average) 2m/s or to put it another way it looses (so -) 2m per second per second or -2m/s/s or in standard form : -2m/s