CIE A Level Physics复习笔记5.1.1 Work & Energy
Work Done
- In Physics, work is done when an object is moved over a distance by an external force applied in the direction of its displacement
- In the diagram below, the man’s pushing force on the block is doing work as it is transferring energy to the block (increasing its kinetic energy)
Work is done when a force is used to move an object over a distanc
- When work is done, energy is transferred from one object to another
- Work done can be thought of as the amount of energy transferred, hence its units are in Joules (J)
- Usually, if a force acts in the direction that an object is moving then the object will gain energy
- If the force acts in the opposite direction to the movement then the object will lose energy
Worked Example
The diagram shows a barrel of weight 2.5 × 103 N on a frictionless slope inclined at 40° to the horizontal.
A force is applied to the barrel to move it up the slope at constant speed. The force is parallel to the slope.What is the work done in moving the barrel a distance of 6.0 m up the slope?
A. 7.2 × 103 J B. 2.5 × 104 J C. 1.1 × 104 J D. 9.6 × 103 J
Exam Tip
A common exam mistake is choosing the incorrect force which is not parallel to the direction of movement of an object. You may have to resolve the force vector to find the component that is parallel. The force does not have to be in the same direction as the movement, as shown in the worked example.
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