70015
| Question | Answer |
| The extension is the difference between the length of the spring and its original length. The extension of a spring is directly proportional to the force applied to it, provided the limit of proportionality is not exceeded. The spring constant of a spring is the force per unit extension needed to stretch it. | |
| Fuel economy of road vehicles can be improved by reducing speed of fitting a wind deflector. Average speed cameras are linked in pairs and they measure the average speed of a vehicle. Anti-skid surfaces increase the friction between the car tyre and the road surface. This reduces skids, or even prevents skids altogether. | |
| The weight of an object is the force of gravity on it. Its mass is the quantity of matter in it. An object acted on only by gravity accelerates at about 10m/s2. The terminal velocity of a falling object is the velocity it reaches when it is falling in a fluid. The weight is then equal to the drag force on the object. | |
| A force can change the shape of an object or change its motion or state of rest. The unit of force is the newton (N). When two objects interact they always exert equal and opposite forces on each other. | |
| The resultant force is a single force that has the same effect as all the forces acting on an object. If an object is accelerating there must be a resultant force acting on it. |
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| The bigger the resultant force on an object, the greater its acceleration. The greater the mass of an object, the smaller its acceleration for a given force. F = m x a | |
| Friction and air resistance oppose the driving force of a car. The stopping distance of a car depends on the thinking distance and the braking distance. |
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