A student carries a backpack horizontally at constant speed across the school courtyard
PHYSICS · Single correct · CBSE · Physics · Work and Energy · Work and Energy
Problem
A student carries a 6kg backpack horizontally at constant speed across the school courtyard. Which of the following best explains why the gravitational force does no work on the backpack during this motion?
(a) The backpack moves at constant speed, so no work is done by any force.
(b) The weight of the backpack is balanced by the upward force of the student, so gravitational work must be zero.
(c) The backpack’s displacement is horizontal while the gravitational force is vertical, so the component of the force parallel to the displacement is zero.
(d) Gravity only does work when an object moves vertically in the direction of the force, so during horizontal motion it cannot do work.