Answer to Question #116405 in Quantum Mechanics for Foibe Kambala

Question #116405
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?
1
Expert's answer
2020-05-25T10:57:16-0400

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=1150kgm=1150 kg

Initial velocity is v0=85km/h=23.6m/sv_0=85 km/h =23.6 m/s

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

The acceleration of the car is

a=vv0t=18.0623.66.0=0.924m/s2a=\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=(1150kg)(0.924m/s2)=1062.7NF=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))=2.214104WP=Fv=(-1062.7)(75(5/18))=-2.214*10^4 W


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