Question

. 12 A 1000-kg car can accelerate from rest to speed 25m/s in 10s. What average power must engine of car produce to cause this acceleration?
. 2? . 2.

Answer 1

mass=1000kg

u=0km/hr=0m/s

v=54km/hr=15m/s

work= change in kinetic energy

= 1/2xmxv^2 - 1/2xmxu^2

= 1/2x1000x15^2 - 0

=112500 J

power = work/time

= 112500/5 = 22500 J/s=22.5 kw

from firs eqution of motion

v=u+at

u=0

therfore

v=at

15=5a

a=3m/s^2

from second equation of motion

s=ut+/2at^2

0+1/2*3*5*%

s=37.5 m

now v avg=dsance/time=37.5/5=7.5 m/s

gaain in KE=KE fina=KE initial

=1/2mv^2-1/2mv2^2

=1/2*1000*15^=112.5kj