Question

you are late for class. as you walk at increasing speed, which external force does positive work on your body? multiple choice the upward normal force from the ground. static friction from the ground propelling your body forward. the force exerted by your legs on the ground. your weight.

Explanation:

• Normal force: Vertical, displacement horizontal → work = 0 (force ⊥ displacement).
• Static friction: Forward force, displacement forward → work positive (force || displacement, same direction).
• Legs’ force on ground: Force on ground, not body → not external force on body.
• Weight: Vertical, displacement horizontal → work = 0 (force ⊥ displacement).

Answer:

B. Static friction from the ground propelling your body forward.