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# M1 Question - Taking Air Resistance Into Account Watch

1. Hello

I am having trouble answering part of a question. The question is:

"Nathan hits a tennis ball straight up into the air from a height of 1.25m above the ground. The ball hits the ground after 2.5 seconds. Assuming g=10m(s^(-2)), find the speed Nathan hits the ball.

Is your answer likely to be an over- or and underestimate given that you have ignored air resistance?"

I can do the first part no problem. However, I cannot think of how to answer the second part. I have thought about it for a bit now and it seems to depend on loads of factors so that I cannot be sure of the answer.

2. (Original post by Magu1re)
Hello

I am having trouble answering part of a question. The question is:

"Nathan hits a tennis ball straight up into the air from a height of 1.25m above the ground. The ball hits the ground after 2.5 seconds. Assuming g=10m(s^(-2)), find the speed Nathan hits the ball.

Is your answer likely to be an over- or and underestimate given that you have ignored air resistance?"

I can do the first part no problem. However, I cannot think of how to answer the second part. I have thought about it for a bit now and it seems to depend on loads of factors so that I cannot be sure of the answer.

He's need to hit it harder to counter-act the air resistance, to get this to hit the ground in 2.5 seconds...

OPEN THE SPOILERS IF NESSESSARY

Spoiler:
Show
If he didn't hit it harder, then the ball would return earlier, and t > 2.5...

Spoiler:
Show
The speed Nathan hits the ball will be an underestimate.

Hope I helped
3. (Original post by Ian.)
He's need to hit it harder to counter-act the air resistance, to get this to hit the ground in 2.5 seconds...

OPEN THE SPOILERS IF NESSESSARY

Spoiler:
Show
If he didn't hit it harder, then the ball would return earlier, and t > 2.5...

Spoiler:
Show
The speed Nathan hits the ball will be an underestimate.

Hope I helped
Air Resistance would slow the ball down along with the ball's weight as it moves upwards. However, whilst air resistance would then continue to act to decelerate the ball, the ball's weight would then act to accelerate the ball downwards. So how can you tell that, even though it will take a shorter time for the same initial velocity to reach it's maximum height, the ball will return to it's starting point more quickly?

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Updated: December 16, 2010
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