# An electric toy car with a mass of #6 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 #4 m/s#?

##### 1 Answer

Mar 19, 2016

#### Explanation:

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

#P = IV#

#= (7 "V") * (3 "A")#

#= 21 "W"#

The change in kinetic energy for the car is

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

#= 1/2 (6 "kg") ((4 "m/s")^2 - (0 "m/s")^2)#

#= 48 "J"#

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

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

#= frac{48 "J"}{21 "W"}#

#= 2.29 "s"#