Practice question · Multiple choice
A horse pulls a cart. By Newton’s third law the cart pulls back on the horse just as hard. How can the pair ever accelerate?
Hints
- To find the cart’s acceleration, add up the forces on the cart only. Does the cart’s pull on the horse appear in that list?
- Action–reaction forces can never cancel each other: cancellation requires two forces on the same object.
Show the answer
C. The two forces act on different bodies
Why
Each body accelerates according to the net force on it alone. The cart feels the horse’s pull (forward) minus friction; the horse feels the cart’s pull (backward) plus the ground pushing it forward. Both nets can be forward at once.
Practise Newton's Laws of Motion
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