Work Physics Example 4

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Example 4

hard
A child pushes a 20 kg20 \text{ kg} crate 8 m8 \text{ m} across a floor with a 60 N60 \text{ N} horizontal force. Friction exerts 40 N40 \text{ N} opposing the motion. What is the net work done on the crate?

Solution

  1. 1
    Work by the child: Wpush=60×8=480 JW_{\text{push}} = 60 \times 8 = 480 \text{ J}.
  2. 2
    Work by friction (opposing): Wfriction=−40×8=−320 JW_{\text{friction}} = -40 \times 8 = -320 \text{ J}.
  3. 3
    Net work: Wnet=480+(−320)=160 JW_{\text{net}} = 480 + (-320) = 160 \text{ J}.

Answer

Wnet=160 JW_{\text{net}} = 160 \text{ J}
Net work accounts for all forces. Friction does negative work because it opposes the displacement. The net work equals the change in kinetic energy of the crate.

About Work

The transfer of energy that occurs when a force causes an object to move through a distance in the direction of the force, calculated as.

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