Work, Energy and Momentum

Work, Energy and Momentum

1. Thinking distance - It takes time for a driver to react to a situation. During this reaction time the car carries on moving. The thinking distance is the distance travelled in between the driver realising he needs to brake and actually braking.

2. Braking distance - The braking distance is the distance taken to stop once the brakes are applied.

3. stopping distance = thinking distance + braking distance

4. Factors that might increase stopping distance Thinking distance can be increased by: Greater speed Tiredness Alcohol and drugs Distractions Braking distance can be increased by: Greater speed Poor road conditions (icy, wet) Car conditions (bald tyres, poor brakes, full of people)

5. Work done

   • Work done (joules, J) = energy transferred (joules, J
   • Work done (joule, J) = force (newton, N) x distance (metre, m)

6. Gravitational potential energy (GPE)

   • GPE (J) = mass (kg) x gravitational field strength (or 'g') (N/kg) x height (m)
   • Weight (N) = mass (kg) x gravitational field strength (N/kg)

7. Kinetic energy = 1/2 x mass x speed2

   • Work done by brakes = loss in kinetic energy

8. The pendulum

   • When the pendulum bob is at the start of its swing it has no kinetic energy because it is not moving. If however, its gravitational potential energy (GPE) is at a maximum, because it is at the highest point.
   • As the bob swings downwards it loses height. Its gravitational potential energy (GPE) decreases. The work done on the bob by the gravitational force (weight) pulling it downwards increases its kinetic energy. The loss of GPE = the gain in KE.
   • At the bottom of its swing, the bob's kinetic energy is at a maximum and its gravitational potential energy is at a minimum - because it is at its lowest point.
   • As the bob swings upwards it slows down. Its kinetic energy decreases as work is done against its weight. As it gains height the gravitational potential energy increases again.

9. momuntum has magintude and direction