Relative mtion project - confused on velocity mostly

AI Thread Summary
The discussion revolves around a physics problem involving a ball tossed from a height of 1 meter to a peak of 12 meters, and an unidentified object moving underneath at 20 m/s. The key calculations include determining the ball's initial velocity, which was found to be 14.69 m/s, and the total time of flight, calculated as approximately 2.995 seconds. The participant also explored relative motion, noting how the ball and the unidentified object appear to move from each other's perspectives, leading to an initial velocity of 24.82 m/s at an angle of 36.3 degrees. The need for accurate diagrams to represent the motion from different viewpoints was emphasized, along with the importance of confirming calculations and angles. Overall, the discussion highlights the complexities of analyzing relative motion in a physics context.
Secretdude
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Homework Statement



A ball is tossed from 1m above the ground to a total height of 12m. An unidentified object passes directly underneath it at 20m/s at a height of 1m. If the ball lands on the object as it passes underneath, how far away was the unidentified object when the ball was tossed? What was the ball's velocity as it was tossed?

Also, I need to find velocities and distances relative to each object (ball, tosser, unidentified object). This is where the problems lie, if there are any.

Ball (to peak)
Viy=?
Vfy=0
a=-9.81m/s2
y=11m

Ball (fall)
Viy=0
y=-11m

Object
V=20m/s
d=?

Tosser
V=0
d=0

Homework Equations


There are quite a few of these...
Vf2=Vi2+2ad
Vf=Vi+at
d=vt
d=Vit+.5at2

Not sure if I need these...
hmax=(Vo2sin2ø)/2g
R=(Vo2sin(2ø))/g
Then there was one for time of flight, as well as some relating x and y and Vix and Viy to sin and cos, but I don't remember them off the top of my head. :(

The Attempt at a Solution


Using a pair of the two formulas above, I got the fall time to be 1.497s, so total toss and fall time should 2.995s. I got distance to 59.9m. Unfortunately I don't have my papers with me at the moment and I don't remember what I got for Vi.


In addition to finding these, I must construct three pictures: one of what the ball sees, one the tosser sees, and one the unidentified object sees.
The tosser's is simple: ball goes up and comes back down, unidentified object moves under the ball.
The ball's may be a problem: the ball "sees" the tosser go down, then come back up. The unidentified object appears to dip down, the come back up under the ball, correct? Because the ball is the point of reference, how fast does the unidentified object appear to move?
Unknown object: Tosser lays flat on the ground and moves at 20 m/s at the unknown object. The ball appears to have been thrown up so that it appears to move in a semicircle. How fast does the ball travel in each direction?

I think that's everything. If something's missing I can get it tomorrow. This is a made-up problem for a project so there'll probably be something wrong with it.
 
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I didn't check your numbers or anything, but your views on the relativity sound good. I would say "appears parabolic" rather than "appears to move in a semicircle."
 
Thanks. I knew there had to be a better term for that.

I found my papers, so I got 14.69m/s as an initial vertical toss velocity. From this and the rate that, from the object's view, the ball is moving towards the unidentified object, I got an initial velocity of 24.82m/s @ 36.3 degrees. To get that, I used this triangle with the Pythagorean Theorem and arc tangent:

.../ |
.../...|
.../...| 14.69m/s
../...|
/...|
--------
20m/s


Was that the correct way? Should I do it similarly to get how fast the object appears to move towards the ball, from the ball's perspective? If I've done something wrong, it's probably the angle...
 
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