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# Edexcel GCSE add 9

Question | Answer |
---|---|

Why might people take risk? | familiarity, adrenaline rush, |

Define acceleration | (change in velocity)/the time taken = (v-u)/t |

What 2 properties does a vector quantity have? | magnitude ( size) and direction |

How do you calculate the acceleration from a velocity time graph? | the gradient of the graph |

If the resultant force acting on a body is not zero, what will it do? | accelerate in the direction of the force |

What are the 2 possible actions that a body could have if the resultant force on it is zero? | constant velocity or remain stationary |

What is the relationship between force mass and acceleration? | F=mxa |

What is Newtons third law? | When two bodies interact, the forces they exert on each other are equal in size and opposite in direction and that these are known as action and reaction forces |

What 2 forces act on a falling object? | Falling objects are acted on by a downward force (weight) and an upward force (air resistance) and that at the start of the fall the forces are unbalanced and the object accelerates |

What happens to the air resistance as the the speed of an object falling through it increases? | the increase in resistance with an increase in speed for a falling object |

When does terminal velocity occur? | When weight downwards = air resistance upwards |

What is stopping distance? | Total distance travelled between seeing reason to stop and stopping. Stopping distance =thinking distance + braking distance |

What is thinking distance? | Distance travelled between seeing reason to stop and foot touching brake. Thinking distance = speed x reaction time |

What is braking distance? | Distance travelled from time foot hot brakes to when the car stops. |

What factors increase thinking distance? | Driver drinking, drugs, mobile phone use. Anything that increases the reaction time |

What factors increase braking distance? | poor brakes, worn tyres, ice, wet weather, anything that reduces friction between road and tyre |

What methods can be used to express risk? | Fractions, ratios and percentages |

What is the difference between imposed risk and voluntary risk? | Imposed - no choice e.g. going to school on bus. Voluntary risk- a choice e.g. skiing, crossing the road not at a zebra crossing. |

Describe and explain measures designed to reduce the rate of change of momentum of fragile objects, eg passengers on a rollercoaster | Change of momentum acts over a larger time reducing the impact time. So brakes are applied gradually. Accelerating and decelerating forces are calculated to ensure that they will not injure the passenger. |

How can we express force in terms of momentum change? | Force= the rate of change of momentum F= (mv-mu)/t mv = final momentum mu = initial momentum |

Explain how seat belts and air bags work? | Increase the time to decelerate, momentum changes more slowly , reducing the force on the passenger. They stop the passengers hitting windscreen and dashboard. |

How do crumple zones work? | The car crumples and absorbs the energy more slowly in the collision. Increasing the collision time, reducing the collision force (rate of change of momentum is reduced). |

What is the formula for momentum? | Mass x velocity |

What is the unit of momentum? | kg m/s |

What is the units of force? | newtons |

What is a unit of acceleration | m/s/s |

What does the symbol v stand for? | Final velocity |

What does the symbol u stand for? | initial velocity |

Name some computer simulation programmes that would use real force data in order to model ' what if' situations | Flight simulators, car design |