A ball is thrown upward and allow to fall under the influence of gravity. We will ignore the effects of air resistance. We consider three times: Time A, when the ball is first thrown upward, Time B when the ball reaches the peak, and Time C when the ball hits the ground. Rank the power delivered by the gravitational force to the ball at those three times from least to greatest.
a. A=C<B
b. A=C=B
c. B<A=C
d. C<B<A
e. A<B<C
I believe that since the ball has ended up in the same spot, the same amount of power was exerted at points A and C but not at point B. My answer to this problem is C...
Is this thinking correct?
Yes
The answer is (e). The power delvered at A is negative as displacement and force mg are oposite.Power delivered at B is zero and at C it is positive as mg and displacement are in the same direction.
A<B<C
Your thinking is partially correct. However, power is not directly related to the final position of the ball; it is related to the work done on the ball over a given period of time.
To determine the power delivered by the gravitational force at different times, we need to consider the work done by gravity and the time it takes to do that work.
At Time A, when the ball is first thrown upward, the gravitational force does negative work on the ball because the displacement of the ball is in the opposite direction from the force. This means that the power delivered by the gravitational force at Time A is negative.
At Time B, when the ball reaches the peak, its velocity becomes zero momentarily. At this point, the ball stops moving in the direction of the gravitational force, so no work is being done by gravity. This means that the power delivered by the gravitational force at Time B is zero.
At Time C, when the ball hits the ground, the gravitational force accelerates the ball downward, doing positive work on it. This means that the power delivered by the gravitational force at Time C is positive.
Based on this analysis, we can conclude that the power delivered by the gravitational force from least to greatest is as follows: A<C<B.
Therefore, the correct answer is d. C<B<A.