. 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.
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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
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