Question

lester prepares to lift a heavy sack of flour into a customer’s shopping cart. during which part of the action does lester do work?
○ when he applies force to the sack before lifting it
○ when he holds the sack against his chest
○ as he lets go of the sack and it falls onto a cart
○ as he lifts the sack to his chest from the floor

Explanation:

Work in physics is defined as \( W = Fd\cos\theta \), where \( F \) is force, \( d \) is displacement, and \( \theta \) is the angle between them. For work to be done, there must be a force applied in the direction of displacement.

• When he applies force before lifting, there's no displacement (\( d = 0 \)), so no work.
• When holding the sack, force is vertical but displacement is zero (no movement), so \( W = 0 \).
• When he lets go, the force he applies is zero (he's not exerting force during the fall), so no work from him.
• When lifting from floor to chest, he applies an upward force, and the sack moves upward (displacement in the direction of force, \( \theta = 0^\circ, \cos\theta = 1 \)), so work is done.

Answer:

D. as he lifts the sack to his chest from the floor