# An electric toy car with a mass of #5 kg# is powered by a motor with a voltage of #4 V# and a current supply of #5 A#. How fast can the toy car accelerate from rest to #3 m/s#?

##### 1 Answer

Aug 24, 2017

#### Explanation:

Power can be expressed in terms of current and voltage as:

#color(blue)(P=VI)#

- The units of power are
**watts**, where one watt is equivalent to one*joule*(of energy)*per second*. We can use this idea along with the concept of**kinetic energy**to determine the time required to accelerate the toy car to the given velocity.

#color(blue)(K=1/2mv^2)#

**We have the following information:**

#|->m=5"kg"# #|->V=4"V"# #|->I=5"A"# #|->v=3"m"//"s"#

We can calculate power:

#P=(4"V")(5"A)#

#color(blue)(P=20" Joules"//"second")#

Now kinetic energy:

#K=1/2(5"kg")(3"m"//"s")^2#

#color(blue)(K=7.5"J")#

So, we have:

#7.5cancel("Joules")xx(1"second")/(20cancel(" Joules"))#

#=>0.375" seconds"#

#=>color(blue)(~~0.38" s")#