A block of mass m is raised by height h at constant speed. What is the work done by gravity on the block?

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Multiple Choice

A block of mass m is raised by height h at constant speed. What is the work done by gravity on the block?

Work is the dot product of force and displacement, W = F · d. The weight acts downward with magnitude mg, while the block is moved upward by height h, so the displacement is upward. The forces and displacement point in opposite directions (angle 180°), giving W_gravity = (−mg) × h = −mgh. The negative sign means gravity removes energy from the block as it rises, which corresponds to an increase in gravitational potential energy by mgh. If the speed is constant, the lifting agent must do +mgh of work to balance gravity, so the net work is zero.

Work is the dot product of force and displacement, W = F · d. The weight acts downward with magnitude mg, while the block is moved upward by height h, so the displacement is upward. The forces and displacement point in opposite directions (angle 180°), giving W_gravity = (−mg) × h = −mgh. The negative sign means gravity removes energy from the block as it rises, which corresponds to an increase in gravitational potential energy by mgh. If the speed is constant, the lifting agent must do +mgh of work to balance gravity, so the net work is zero.

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