Work – Energy – Power

Worksheet

  1. A woman exerts a horizontal force of 400N on a cart and pushes it horizontally through a distance of 30m. Calculate the work done by the force.
  1. A husky dog does 20kJ of work as he pulls a sleigh with a force of 340N. Through what distance does he pull it?
  1. What is the weight of a mass of 100kg? Find the work done in raising a mass of 100kg through a vertical height of 60m at a constant velocity.
  1. A car of mass 1000kg accelerates from 0 to 80 km/h in 20 seconds. Find the work done.
  1. Find the work done in bringing a car of mass 800kg from rest to a speed of 30m/s in 10s.
  1. A Boeing 747 of mass 360,000kg needs to reach a runway speed of 80m/s in order to take off. What is the kinetic energy at take off?
  1. A pole-vaulter has a mass of 80kg and raised his centre of gravity 30 cm above a bar 6.14m high. What was his maximum potential energy during the vault?
  1. A gymnast swings back and forth on the end of a 4m long rope that is attached to the ceiling of a gymnasium. If at the highest point of each swing she is 1.5m from the ceiling, what is her maximum speed?
  1. A boy throws a €1 coin from the top floor of the Empire State Building which is 370m above the ground. The mass of the €1 coin is 7.5g.
  1. What is the kinetic energy of the coin just before it hits the pavement, ignoring the friction due to the air?
  1. At what speed does the coin hit the pavement?
  1. A football of mass 400g is dropped from a height of 1.6m and bounces to a height of 1.2m
  1. What speed does it strike the ground?
  1. How much energy is lost when it bounces?
  1. As energy is never created or destroyed, what happened the ‘lost’ energy?
  1. Given that its maximum potential energy on bouncing to a height of 1.2m is 4.704J, at what speed did it leave the ground?
  1. A bullet of mass 4 g with a velocity of 200 m/s penetrates 0.5m into a block of wood. Find the force that the wood exerts on the bullet. Calculate the velocity with which the bullet emerges if the block is only 0.25m thick, assuming the same opposing force.
  1. A pendulum bob of mass, m is released from a height of 0.5m. Find the speed of the bob as it passes through the vertical position.
  1. A car has a maximum power of 130kW. While operating at this power how much energy does it expend in 5 minutes?
  1. A weight lifter raises a mass of 50kg through a height of 2m. He does this 25 times in one minute. Find his average power.
  1. A boy of mass 40kg sprints up 50 stairs each of height 16cm in 40s. Find his average power.
  1. An empty lift has a weight of 7900N and is powered by an electric motor. The lift takes three people, each weighing 700N , up 45m in 60s. Calculate:
  1. The work done by the lift’s motor
  1. The power output of the motor
  1. If the lift operates with a 9kW motor. What is the efficiency of the motor?