Relative mtion project - confused on velocity mostly

In summary, the problem involves a ball being tossed from 1m to a height of 12m, while an unidentified object passes underneath it at 20m/s and a height of 1m. The goal is to find the distance of the unidentified object from the ball when it was tossed and the ball's initial velocity. The equations used include Vf2=Vi2+2ad, Vf=Vi+at, d=vt, and d=Vit+.5at2. The toss and fall time were found to be 2.995s, and the distance to be 59.9m. The ball's perspective shows a parabolic path, while the tosser's perspective shows a simple up and
  • #1
Secretdude
2
0

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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  • #2
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."
 
  • #3
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...
 
Last edited:

Related to Relative mtion project - confused on velocity mostly

1. What is relative motion and how does it differ from absolute motion?

Relative motion is the movement of an object in relation to another object or reference point. It differs from absolute motion because absolute motion refers to the movement of an object in relation to a fixed point, such as the Earth's surface.

2. How do you calculate velocity in a relative motion project?

To calculate velocity in a relative motion project, you need to determine the displacement (change in position) of the moving object and divide it by the time it takes to make that displacement. Velocity is a vector quantity and includes both magnitude (speed) and direction.

3. Can you explain the concept of relative velocity?

Relative velocity is the velocity of an object in relation to another object. It takes into account the velocity of both objects and can be calculated by subtracting the two velocities. For example, if two cars are moving in opposite directions, the relative velocity between them would be the sum of their individual velocities.

4. What factors can affect the relative motion of objects?

The relative motion of objects can be affected by factors such as the speed and direction of the objects, the distance between them, and any external forces acting on them, such as friction or gravity.

5. How is relative motion applied in real life?

Relative motion is applied in many areas of science and engineering, such as in the design of vehicles and aircraft, understanding the motion of planets and satellites, and calculating the effects of wind and water currents. It is also used in everyday situations, such as navigating through traffic or playing sports.

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