An electric toy car with a mass of #4 kg# is powered by a motor with a voltage of #7 V# and a current supply of #3 A#. How long will it take for the toy car to accelerate from rest to #7/2 m/s#?

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Answer 1 · 2017-08-14T15:32:10

The time is #=1.17s#

The power is

#P=UI#

The voltage is #U=7V#

The current is #I=3A#

The power is

#P=UI=7*3=21W#

The kinetic energy of the car is

#E=1/2mv^2#

The mass is #m=4kg#

The speed is #v=7/2ms^-1#

so,

#E=1/2*4*(7/2)^2=49/2J#

Let the time #=ts#

#E=Pt#

#t=E/P=(49/2)/21=1.17s#