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

2 Answers
Jul 17, 2017

The time is #=0.11s#

Explanation:

The power is

#P=UI#

The voltage is #U=3V#

The current is #I=7A#

The power is

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

The kinetic energy of the car is

#E=1/2mv^2#

The mass is #m=2kg#

The speed is #v=3/2ms^-1#

so,

#E=1/2*2*(3/2)^2=2.25J#

Let the time #=ts#

#E=Pt#

#t=E/P=2.25/21=0.11s#

Jul 17, 2017

t= 0,107 s

Explanation:

the final kinetic energy of the car is #E_K = 1/2 mv^2 = 1/2 2 kg xx (1,5 m/s)^2= 2,25 J#
the power supplied is #P= V xx I=3 V xx 7A = 21 W#
since P=E/t you have #t = E/P = (2,25J)/ (21 W) = 0,107 s #