Question

A toy train of mass $1kg$ moves with a constant velocity of $8m/s$ when connected to a battery of $8V$. Find the current in the circuit if the battery was connected for $4s$. Assume no energy loss due to friction.

• A. 1 A
• B. 2 A
• C. 3 A
• D. 4 A

Answer 1

The correct option is A

1 A

Electrical energy of the battery will be converted into mechanical energy.

Kinetic energy of the train = $\frac{1}{2}m{v}^2$ = $\frac{1}{2}\times 1\times 8^2$ = $32J$

This energy should be equal to the energy produced by battery which is $W=qV$

$qV=32J$

$q$ = $\frac{32J}{8V}$ = $4C$

Now current, $I$ = $\frac{q}{t}$ = $\frac{4C}{4s}$ = $1A$