3 Conservation of energy

An electric lawnmower is used to cut grass. During each second of use, the energy supplied to the lawnmower is transferred in the ways shown.

Energy transfer	Energy transferred
to the kinetic energy store of the blades	550 J
to the thermal energy stores of the motor and surroundings	400 J
by sound	50 J

What is the efficiency of the lawnmower?

[1]

$45%45\%$

$55%55\%$

$58%58\%$

$92%92\%$

An electric lawnmower is used to cut grass. During each second of use, the energy supplied to the lawnmower is transferred in the ways shown.

Energy transfer	Energy transferred
to the kinetic energy store of the blades	550 J
to the thermal energy stores of the motor and surroundings	400 J
by sound	50 J

What is the efficiency of the lawnmower?

[1]

$45%45\%$

$55%55\%$

$58%58\%$

$92%92\%$

3 Conservation of energy Questions