Work and Power: Answers

 

A gardener pushes a wheelbarrow down his garden path, which has a total distance of 10 meters. He exerts 200 N of force. Calculate the work done on the wheelbarrow.

  • Work done (J) = force (N) x distance (m)

  • Work done = 200 x 10 = 2000 J

A book weighing 350 g was placed on a bookshelf two meters from the floor. Calculate the gain in gravitational potential energy. The gravitational field strength on Earth is 10 N/kg.

  • Gravitational potential energy (J) = mass (kg) x gravitational field strength (N/kg) x height (m)

  • Convert mass from grams to kilograms. 350 g = 0.35 kg

  • GPE = 0.35 x 10 x 2 = 7 J

A 30 kg girl is rollerblading at a speed of 15 m/s. Calculate her kinetic energy.

  • Kinetic energy = 0.5 x mass (kg) x speed2 (m/s)
  • KE = 0.5 x 30 x 152
  • KE = 3375 J

A hairdryer transfers 6 kJ of useful energy in two minutes. Calculate its power.

  • Power = work done (aka energy transferred) / time taken

  • Convert work done from kJ to J. 6 kJ = 6000 J.

  • Convert mins to seconds. 2 mins = 120 seconds.

  • Power = 6000 / 120 = 50 W