Question

An electric toy car with a mass of `5 kg` is powered by a motor with a voltage of `1 V` and a current supply of `6 A`. How long will it take for the toy car to accelerate from rest to `4/5 m/s`?

Answer 1

It will take only 0.27 s to reach this speed.

Explanation:

This problem will be solved using energy considerations, demonstrating the ease with which energy connects different situations - electrical and mechanical.

Given the current and voltage supplied to the motor, we can calculate the power output:

`P=IxxV = 6` watts

This means that work is being done on the car at a rate of 6 joules per second.

For the rest of the problem, we will continue to work in energy terms.

The kinetic energy of the car, must change from zero to

`K=1/2 mv^2 = 1/2 (5)(4/5)^2= 1.6 J`

Since work is being done at 6 J/s, the time required will be:

`(1.6 J)/(6J/s) = 0.27 s`