A girl holds a stone in her hand and can move it up or down or keep it still. Which of the following statements are true? (Select all that apply.) None of these statements are true. If the girl moves her hand downward but slows the stone to rest, the force of the stone on the girl's hand is the same magnitude as the force of gravity on the stone. The force exerted by her hand on the rock is the reaction force to the force of gravity on the stone. If the girl moves her hand down at a constant speed, then her upward force on the stone is less than the force of gravity on stone. The force exerted by her hand on the rock is always the same magnitude as the force of gravity on the stone. The force exerted by her hand on the stone is always the same magnitude as the force on her hand by the stone, but in the opposite direction.

Question

Cosmo

Physics

25 September, 16:06

A girl holds a stone in her hand and can move it up or down or keep it still. Which of the following statements are true? (Select all that apply.) None of these statements are true. If the girl moves her hand downward but slows the stone to rest, the force of the stone on the girl's hand is the same magnitude as the force of gravity on the stone. The force exerted by her hand on the rock is the reaction force to the force of gravity on the stone. If the girl moves her hand down at a constant speed, then her upward force on the stone is less than the force of gravity on stone. The force exerted by her hand on the rock is always the same magnitude as the force of gravity on the stone. The force exerted by her hand on the stone is always the same magnitude as the force on her hand by the stone, but in the opposite direction.

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Ronin Durham · Answer 1

Answer: The true statements is " the force exerted by her hand on the stone is always the same magnitude as the force on her hand by the stone, but in the opposite direction".

Explanation:

If the girl moves her hand downward but slows the stone to rest, the force of the stone on the girl's hand is the same magnitude as the force of gravity on the stone.

This statement is false because there is an acceleration if she is slowing the stone. Then there will be net force acting on it.

The force exerted by her hand on the rock is the reaction force to the force of gravity on the stone.

This statement is false because in the given problem, the reaction force to pull gravity is the force exerted on the rock.

If the girl moves her hand down at a constant speed, then her upward force on the stone is less than the force of gravity on stone.

This statement is false because the speed is constant then the net force acting on the stone must be zero.

The force exerted by her hand on the rock is always the same magnitude as the force of gravity on the stone.

This statement is false because the force exerted by the girl must be greater than the weight of the stone if the rock is accelerating.

The force exerted by her hand on the stone is always the same magnitude as the force on her hand by the stone, but in the opposite direction.

This statement is true because this is according to Newton's third law which is stated as "for every action, there is an equal and opposite reaction".

Therefore, "the force exerted by her hand on the stone is always the same magnitude as the force on her hand by the stone, but in the opposite direction" is true.