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| Question | Answer |
| P3c - Forces and Motion | . |
| If the forces acting on an object are balanced, it's at rest or has a constant speed.If the forces acting on an object are unbalanced, it is slowing down or speeding up. | Force(N) = mass x acceleration F = unbalanced force in N M = mass in kg A = acceleration in m/s^squared |
| Worked example: | Marie pulls a sledge of mass 5kg with an acceleration of 2m/s^squared in the snow. The force needed to do this is: F= M x A 5 x 2 = 10N |
| Stopping Distances | stopping distance = thinking distance + braking distance |
| Thinking Distance | It takes time for a driver to react to a situation and start to apply the brakes. The car carries on moving during this reaction time. The thinking distance is the distance travelled in this reaction time. The thinking distance increases if the reaction time increases. This can happen if the driver is: - Tired - Distracted or not concentrating - Under the influence of alcohol or other drugs. The thinking distance also increases as the car's speed increases (as the car will travel further during the reaction time). |
| Breaking Distance | The braking distance is the distance taken to stop once the brakes are applied. The braking distance increases if: - The car's brakes or tyres are in poor condition - The road and weather conditions are poor (icy or wet roads, for example). The braking distance also increases as the car's speed increases. |
| Continue... | The thinking distance increases linearly with speed. The braking distance increases as a squared relationship with speed: - If the speed doubles, the braking distance increases four times - If the speed trebles, the braking distance increases nine times and so on. This is because the kinetic energy of the car also has a squared relationship with speed |
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