The electric motor of a model train accelerates the train from rest to 0.685 m/s in 21.5 ms. the total mass of the train is 875 g. find the minimum power delivered to the train by electrical transmission from the metal rails during the acceleration.

P=9.58 W

Explanation:

According to Newton's second law, and assuming friction force as zero:

The acceleration is given by:

So the force exerted  by the motor is:

The work done by the motor is given by:

And finally, the power is given by:

the body's situation won't change the forces are equal opposit and on the same body

the minimum constant speed at which she can catch the train is 2.7 m/s

given:

acceleration = 0.6

time = 4.5 s

to find:

velocity = ?

formula used:

from 1st kinematic equation we get,

v = u + at

u = initial speed of train = 0 m/s

v = final speed of the train

a = acceleration of the train

t = time

solution:

from 1st kinematic equation we get,

v = u + at

u = initial speed of train = 0 m/s

v = final speed of the train

a = acceleration of the train

t = time

v = 0 + (0.6 × 4.5)

v = 2.7 m/s

the minimum constant speed at which she can catch the train is 2.7 m/s