Question

The electric motor of a model train accelerates the train from rest to 0.620m/s in 21.0ms.? The total mass of the train is 875g. a) Find the minimum power delivered tothe train by electrical transmission from the metal rails during the acceleration. b) Why is it the minimum power?

I know how to do the average power, but this asking for minimum power, which sounds like instantaneous power to me. I know how to calculate the acceleration, which Iam assuming is constant, and force. I don't know what velocity to use to get minimum power. I obviously don't know how to answer why it is the minimum power. Pleasehelp.

Answer 1

GIVEN:

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(a)
mass of the train =875g =875*10^-3 kg
since ,the train accelerate from the rest positin its intial velocity(U)=0
gaining velocity (V)= 0.62m/s
during the time intervel(t)=21 ms=21*10^-3 s
by the def. of acceleration ,
we have,
acceleration(a)=( V-U)/t
=(0.62-0)/12*10^-3 m/s^2
=51.66 m/s^2
the force acting on the model train F= m.a
=875*10^-3(51.66)
=45.2 N
thus, the minimum power delivered to the train by electrical transmission from the metal rails during this acceleration should be equal to the force actingon the model train
so, the minimum power (P)= 45.2 J

(b) since the power is acting on the model train for very lesser time (i.e in the order of millisec.)