Calculate the height above the lowest point which the pendulum will reach.

Physics by Geoffrey

Tutorial 9 Energy, Work & Power

  1. A head-on collision between two objects results in these two objects coming to rest

completely.

The following are descriptions of possible candidates for this collision. Say whether each is a                   possible or impossible situation which fulfils the condition. In each case give

fully detailed            reasons.

  1. Two perfectly elastic balls of the same mass arriving with equal but opposite velocities.
  2. A collision between two objects which results in destruction of 75% of the total

kinetic                                 energy.

  1. A collision between an object of mass 5 kg and one of 15 kg.
  2. A collision between an object of momentum 5 kg ins-1 and one of —7.5 kg ms-1.
  3. A collision between an object of kinetic energy 17 J and one of kinetic energy 27
  4. A bullet is fired vertically upwards with a speed of 120 ins-1. What is the maximum

height it can reach?

  1. The Niagara Falls are about 50 m high. It is estimated that 100 million kilograms of

water pour over the falls every second. If 50% of this energy could be harnessed how much power would be     available?

  1. In loading a lorry a man lifts boxes each of weight 100 N through a height of 1.5 in.
  2. How much work does he do in lifting one box?
  3. If he lifts 4 boxes a minute at what power is he working?
  4. The pendulum of a clock passes its lowest point at a velocity of 0.7 ms-1.

Calculate the height above the lowest point which the pendulum will reach.

  1. When you learn to drive you need to be able to judge your stopping distance. This is

made up of 2 parts. Your thinking distance where you keep travelling at your original speed while you react to a problem (a slow reaction time would be 0.7 seconds). Then your braking distance where the brakes act to remove the car’s kinetic energy.

Speed (ms-1) 10 20 30 40
Thinking distance (m)   14    
Braking distance (M) 10   90  
Total distance (m)       188

 

  1. Assume your reaction time is 0.7 seconds. Complete the thinking distance values.
  2. Suppose you and your car have a mass of 1 200 kg. When the brakes are applied

carefully                   a force of 6 000 N is applied to the wheels.

  1. Using the idea that the brakes do work to remove kinetic energy, show that

the                                       car’s braking distance, at an initial speed of 10 ms-1, is 10 m.

  1. Complete the rest of the table.
  2. If three passengers are given a lift, the mass increases to 1 500 kg. What

difference does                              this make to your total stopping distance?

  1. What difference does it make to your stopping distance if you are travelling

downhill.                            Explain your answer in terms of energy changes.

  1. A crate is pushed 10 m along a horizontal surface by a force of 80 N. The frictional force

opposing the motion is 60 N.

  1. Calculate the total work done.
  2. Calculate the heat energy produced.
  3. Calculate the kinetic energy gained by the crate.