Answer to Question #116405 in Quantum Mechanics for Foibe Kambala

Question

9. A driver notices that her 1150 kg car slows down from 85 km/h to 65 km/h in about 6.0 s
on the level when it is in neutral. Approximately what power (Watts and hp) is needed to
keep the car travelling at constant speed of 75 km/h?

Answer 1

9. A driver notices that her 1150 kg car slows down from 85 km/h to 65 km/h in about 6.0 s

on the level when it is in neutral. Approximately what power (Watts and hp) is needed to

keep the car travelling at constant speed of 75 km/h?

Given data

Mass of car is $m=1150 kg$

Initial velocity is $v_0=85 km/h =23.6 m/s$

Final velocity is $v=65 km/h=18.06 m/s$

The acceleration of the car is

$a=\frac{v-v_0}{t}=\frac{18.06-23.6}{6.0}=-0.924 m/s^2$

The force acting on the car is

$F=ma=(1150 kg)(-0.924 m/s^2)=-1062.7 N$

The amount of power is needed to keep the car travelling at constant speed of 75 km/h is

$P=Fv=(-1062.7)(75(5/18))=-2.214*10^4 W$