Acceleration Question (NOVA Ch 4, Passage 1 #3)

[pwad]

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Hey guys, I just needed help with the reasoning behind this one:

From the passage: "A student accelerates uniformly from rest at one side of the building to the jumping edge."

Question: Which diagram best represents the force diagram from the student while he is on the roof?

So, I had narrowed it down to either the figure with
A) only Fn and Fg acting on it
B) Fn, Fg, and a forward force too
(the correct answer is B)

My Reasoning:
While I realize that the student is uniformly accelerating before jumping, I thought uniform acceleration meant a=0, so the F to the right:
F=ma --> F=m(0) = 0, or no forward force (and only Fg and Fn)

My reasoning is incorrect. Can someone please explain why?

 

[loveoforganic]

Uniform acceleration could technically be 0, but generally it would be referring to a non-zero number. Think gravity on earth's surface - a = 9.8, constant.

 

[stsa84]

Yeah, uniform acceleration only means that the rate of acceleration stayed the same, as in, he kept accelerating at a constant rate of 0.5 m/s or something.

 

[pwad]

ahhh okay, so F=m(non-zero number)= non-zero force
Thanks for the clarification!