Which of the following statements is/are incorrect regarding work?

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Positive work: A ball being thrown upwards by a kid.

Negative work: Work done by the gravitational force of the earth on a ball thrownupwards.

Zero work: Sliding of a box on the ground when the gravitational force acts on the box.

None of the above

answer is D.

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Detailed Solution

All of the options are correct.
When a force acts in the body's direction of motion, it is called positive work. For example, when a ball is thrown upwards by a kid, the direction of the force exerted by the kid and the direction of motion of the ball is upwards. Hence, option (1) is correct.
When a force acts opposite to the body's direction of motion, it is called negative work. For example, the direction of the earth's gravitational force is downwards, while the ball's direction of motion is upwards. Hence, option (2) is correct.
When a force acts perpendicular to the body's direction of motion, then the work done is zero. For example, the box slides forward on the ground when the downwards gravitational force acts on the box. Due to the force and displacement being perpendicular to one another, zero work is done. Therefore, option (3) is also correct.

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