Respuesta :
Answer:
If the system consists of the block only, the work done by the gravity is negative.
If the system consists of the block and the earth the work done by the gravity is zero.
Explanation:
If the system consists of the block only, then the system experiences two external forces: one exerted by the hand that lifts the block vertically upward and other exerted by the earth (gravity), which is opposed to the movement of the system, so the work done by gravity is negative.
On the other hand, if the system consists of the block and the earth, then only exists a external force which is the exerted by the hand. So, the force exerted by gravity is zero.
A) For the block only, the work done by gravity on the block; is negative
B) For the block and earth system, the work done by the gravity on the block; is zero
A) We are told that the block is raised vertically. This means that work done by the force due to a height h will be given by;
W = Fh
Now, the work done by gravity will be equal and opposite to the work done by force F since the block is moving with constant velocity.
Gravity acts downwards and as such the opposite which is work done by the force acting upwards will be negative.
B) For the block and earth system, the work done by gravity on the block-earth system will be zero. This is because there is no gravitational force being exerted on the system by any external object.
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