My physics final is tomorrow with mostly conceptual questions. I amconfused abou
ID: 1729691 • Letter: M
Question
My physics final is tomorrow with mostly conceptual questions. I amconfused about some of our post-test questions, as was ourprofessor (go figure). The question was something along the linesof "Which forces are present on a baseball being thrown straight upinto the air after it has left the hand? Wind is negligible."I know gravity acts down on it. I assumed that was it, hence whythe ball returns to earth. But the multiple choice answers for allthese "Which forces are present?" questions all had a confusingconcept as an answer to trick you.
I.e. "Which forces are present on a baseball being thrown straightup into the air after it has left the hand? Wind isnegligible."
A) Gravity
B) Gravity and a decreasing upward force until the ball reaches itsapex.
The questions says "After it has left the hand" so I assume theanswer is simply gravity. I asked my teacher and he thinks B iscorrect because the ball continues upward (meaning it still has anet upward force) until it reaches its peak. There were lots ofthese force questions and all had a confusing answer where themomentum was considered a force acting on an object, just becauseit was in motion? Is this right?
Explanation / Answer
you were right and your instructor was wrong (go figure :) The only force that acts on the baseball is gravity. The reason itkeeps moving up was because its initial velocity was in thatdirection. But hey, if you notice its slowing down and after someheight it comes to a stop. Why would it come to a stop? Well because there is an opposinggravitational force acting on it and that force is pulling itdownward. Just because a body is moving in a certain direction does not meanthere is a hidden force thats pushing it in that direction. If that body is accelerating in that direction (say a sportscar ona road) , yes there is a force thats thrusting it forward. But if the body is decelerating (in the case of the ball goingupward), the force is actually acting opposite to the motion. Lemme know if you've more questions. Good luck on the test!
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