Question

When a current of 2.0 A is supplied to a motor which is used to drive a machine, a mass of 2.0 kg is lifted up for 5.0 m in 2.0 s in a uniform velocity. Assuming that the machine is 100 % efficient, what is the potential difference across the terminals of the motor?

Answer 1

Mass of the body, $m=2\space kg$

Distance lifted, $s=5\space m$

Time, $t=2\space s$

Work done,$W$ = $mgs=2\times10\times5=100\space J$

Power = $\dfrac{W}{t}=\dfrac{100}{2}=50\space J/s$

Let potential difference across the motor be $V$

Current supplied, $I=2\space A$

Power supplied by the motor, $P=VI$

Since the machine is 100 % efficient

$\therefore VI=50$

$V=\dfrac{50}{I}=25\space V$

Potential difference across the terminals of motor = 25 V