Question

a car is moving with the speed of 72km/h is brought to rest in 10 sec by applying brakes. find the magnitude of the average retardation due to the brakes and the distance travelled after applying the brakes

Answer 1

Answer:

a=-2m/s square,s=100m

Explanation:

from equation 1

v=u+at

0=20+10a

-20=10a

a=-2m/s^2

from equation 3

2as=v^2-u^2

-4s=-400

s=100m

Answer 2

Answer:

Average retardation=-7.2m/s square

Distance travelled=560m/s

Explanation:

Initial velocity ,u=72km/h

=72×5÷18=20m/s

Final velocity,u=0(As the car applied brakes.)

Retardation =Final velocity-Initial velocity÷Time

=72-0÷10=-7.2m/s square

Distance travelled after applying brakes,s

=s=ut+1÷2at square

=s=20×10+1÷2×7.2×10×10

=200+7.2×10×5

=560m/s