# Homework Help: If you toss a tennis ball straight upward, shouldn't there be in horiz

1. Feb 17, 2013

### cmkc109

1. The problem statement, all variables and given/known data

If you toss a tennis ball straight upward, shouldn't there be in horizontal motion of the ball?

The question says a bus is travelling north, u toss a ball directly upward, will it collide with the thrower.
The answer says : The ball is in motion horizontally and that horizontal component will continue (as stated in the first law of motion). Thus,
the ball will not collide with the thrower. In this case, we assume that air resistance on the ball is negligible. (If the
thrower tried the same experiment while on a motorcycle, the result would be much different because of air resistance.)

BUT I Thought there is no horizontal force if u throw it directly upward

2. Feb 17, 2013

### deblimp

Re: If you toss a tennis ball straight upward, shouldn't there be in h

This is a question about inertial frame of reference. The ball is not moving horizontally when you throw it up, relative to you. It is moving relative to the ground int the same direction and at the same speed as everyone and everything else on the bus is. If an outside observer were to watch this happen the ball would appear to move in an arc. The ball would travel some distance horizontally, but so would everyone else on the bus. Since there are no horizontal forces acting on the ball there is no reason why it would deviate from its horizontal velocity which is zero relative to the person throwing the ball. Therefore it wouldn't hit you in the face.

3. Feb 17, 2013

### SammyS

Staff Emeritus
Re: If you toss a tennis ball straight upward, shouldn't there be in h

Please give the question exactly as worded.

Does it really say
"u toss a ball directly upward" ?​

4. Feb 17, 2013

### cmkc109

Re: If you toss a tennis ball straight upward, shouldn't there be in h

Yes, "I" toss it

5. Feb 17, 2013

### SammyS

Staff Emeritus
Re: If you toss a tennis ball straight upward, shouldn't there be in h

Are you riding on the train?

I repeat:
Please give the question exactly as worded.​
The complete question.

6. Feb 17, 2013

### cmkc109

Re: If you toss a tennis ball straight upward, shouldn't there be in h

You are sitting on a bus that is travelling at a constant velocity of 55 km/h [N]. You
toss a tennis ball straight upward and it reaches aheight just above the level of your

7. Feb 17, 2013

### SammyS

Staff Emeritus
Re: If you toss a tennis ball straight upward, shouldn't there be in h

Now that we have that straightened out, what is troubling you?

8. Feb 17, 2013

### cmkc109

Re: If you toss a tennis ball straight upward, shouldn't there be in h

my question is on the top.
why is there horizontal velocity when it is thrown upward. is it because of the frame of reference that the other user suggests?

9. Feb 17, 2013

### SammyS

Staff Emeritus
Re: If you toss a tennis ball straight upward, shouldn't there be in h

In the reference frame attached to the (constant velocity) bus, the horizontal component of the ball's velocity is zero. The ball goes directly up, and directly back down, both motions completely vertical .

In the reference frame attached to the ground, the ball has a horizontal component of velocity which matches that of the bus (also matches your horizontal component of velocity). The ball's motion in the horizontal direction matches your motion.

From your point of view, riding on the bus, the motion of the ball is the same no matter whether the bus is stationary, or is moving with a constant velocity.

10. Feb 18, 2013

### CWatters

Re: If you toss a tennis ball straight upward, shouldn't there be in h

The question implies you are throwing the ball up vertically with respect to you and the bus.

Consider this question..

"You are standing on the ground 3m away from your house. You toss a tennis ball straight upward and it reaches a height just above the level of the top floor window. Will the ball collide with your house?"

You would probably answer no because you threw it straight up and that would be correct. The fact that the earth surface is moving at 1000mph won't make a difference because you threw it straight up relative to you, the house and the surface of the earth. The ball starts with a horizontal velocity of roughly 1000mph.