1001 EK Physics problem124

[jekim3]

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124
one man drops a rock from a 100m building. At Exactly the same moment, a second man throws a rock from the bottom of the building to the top of the building. At what height do the rocks meet?



tried so many times and even checked answer ,but I could not understand.
Please help

 

[loveoforganic]

I believe that would be impossible to answer without the initial velocity of the rock being thrown upward.

 

[jekim3]

no initial velocity of rock thrown can be solved by v^2 = vo^2 +2ad
but even with initial velocity, the problem can't be solved.

 

[loveoforganic]

You are not given any of the information in that equation... So no, initial velocity could not be solved for in that manner. It has to be given to you. And if it were given to you, it would be solvable.

 

[TheBoondocks]

124
one man drops a rock from a 100m building. At Exactly the same moment, a second man throws a rock from the bottom of the building to the top of the building. At what height do the rocks meet?



tried so many times and even checked answer ,but I could not understand.
Please help

this would never show up on mcat. However, it's still a ^ problem for elucidating the thought process.

I always use delta x= vot + etc. Using that here is bad

The key to this problem is realizing that the ball is thrown so that it will reach 100m. I didn't see this at first, however, you must think mcat so ideas like this should enter your head.

x=xo + vot + .5gt^2. for thrown rock. xo=0. So, x= vot -.5gt^2 for thrown

for dropped x=100 - .5gt^2. These distances are equal, since the x is equal to the distance the thrown one travels and is equal to the distance at which the second rock is at.

Set them equal, 100=vot vo=2000^.5 which is basically 45

100/45 is about 2.2 2.2^2 is 4.84 but you know it's less than 5. so using t=2.3, we solve for x, 100-.5(5)(10)= 75

This is a little BS because since it was translational, i didn't think I'd need energy, but it's good in a way because it lets you see the advantage of energy problems. It showed me the importance of understanding the equations.

 

[loveoforganic]

The key to this problem is realizing that the ball is thrown so that it will reach 100m.

Nice catch

 

[hellohumph]

i think that last catch had a problem.

when you say vot=100 that would only be if a=0

so the calculation would still not make sense.

also, when you say the x values are equal... one should be x and the other should be 100-x because it is the point they meet, not their traveled heights.

 

[zhemnis]

guys it must be 25m think logically

 

[brood910]

guys it must be 25m think logically

This post is 4 years old. Think logically.