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 #8 A#. How long will it take for the toy car to accelerate from rest to #7/2 m/s#?

1 Answer
Mar 20, 2016

#0.4375 "s"#

Explanation:

The power input is the product of the voltage and the current.

#P = IV#

#= (7 "V") * (8 "A")#

#= 56 "W"#

The change in kinetic energy for the car is

#Delta "KE" = 1/2 m (v^2 - v_0^2)#

#= 1/2 (4 "kg") ((7/2 "m/s")^2 - (0 "m/s")^2)#

#= 24.5 "J"#

Thus, the time needed is the energy divided by the power.

#t = frac{Delta "KE"}{P}#

#= frac{24.5 "J"}{56 "W"}#

#= 0.4375 "s"#