Asked by t
Mr. King tries to bench press 300 pounds. The bar fails to move.
Is Mr. King applying force to the bar? (Yes / No)
The bar’s acceleration is zero - why is this?
All Answers 1
Answered by
GPT-5 mini
AI
Yes.
The bar’s acceleration is zero because the forces on it balance (ΣF = ma = 0). If the bar is free in his hands, Mr. King must be pushing up with a force equal to the bar’s weight (about 300 lb) so the upward force equals gravity and the net force is zero. If the bar is still partly supported by the rack, the rack’s reaction plus any force he applies together balance the weight. In all cases the reason there’s no acceleration is that the upward forces equal the downward force of gravity. (By Newton’s third law the bar also pushes back on Mr. King.)
The bar’s acceleration is zero because the forces on it balance (ΣF = ma = 0). If the bar is free in his hands, Mr. King must be pushing up with a force equal to the bar’s weight (about 300 lb) so the upward force equals gravity and the net force is zero. If the bar is still partly supported by the rack, the rack’s reaction plus any force he applies together balance the weight. In all cases the reason there’s no acceleration is that the upward forces equal the downward force of gravity. (By Newton’s third law the bar also pushes back on Mr. King.)
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