A truck weighing 1000 kgf changes its speed from 36 km per hour in 2 minutes. Calculate:
1) The work done by the engine and its power

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Solution

Given:
w=1000kg(force exerted by 1000kg) mass
m=1000kg
u=36km/hr= 36x 5/18= 10 m/ s
v=72km/ hr= 72x 5/18=20 m/s
t=2min =2x 60 = 120 secs.
we know that:
w= F x s
F= mxa
a=v-u/ t = (20-10)/120= 1/12 m/ s^2.
v^2- u^2= 2as
(v-u)(v+u)=2x (v-u)x s/ t
s=1/2(v+u) x t= 1/2 (20+10)x 120=1800m
w=mxaxs
=1000 x 1x 1800/12=1.5 x10^5 J
Power=work done/ t
=1.5 x 10^ 5/120=1.25 x 10^3 watts (answer)
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