Projectile and relative motion help

  • Thread starter Torpedo007
  • Start date
  • #1

Homework Statement



A boy is standing on a long railroad car throws a ball straight upwards.The car is moving on a horizontal road with an accelaration of 1m/s^2. and the projection velocity is 9.8m/s.How far behind the boy will the ball fall on the car.

Homework Equations


Not entirely sure what to use but i tried using the basic equations of motions and relative velocity but without an actual velocity for the rail car i found it really hard


The Attempt at a Solution



I fist used the basic V=U+at and found the time taken to go up.

Hence time taken to come down will be 2t.In this same the car should have travelled a certain distance.Now this is where im stuck since i only have the acceleration not the speed of the car D:

I juggled around but couldnt get the proper answer which was 2 meters

Any help would be much appreciated!
 
Last edited:

Answers and Replies

  • #2
tiny-tim
Science Advisor
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Welcome to PF!

Hi Torpedo007! Welcome to PF! :smile:

(try using the X2 icon just above the Reply box :wink:)

Show us what you've tried, and where you're stuck, and then we'll know how to help! :smile:
 
  • #3


Hi Torpedo007! Welcome to PF! :smile:

(try using the X2 icon just above the Reply box :wink:)

Show us what you've tried, and where you're stuck, and then we'll know how to help! :smile:

Hey thanks for the reply ;D

I fist used the basic V=U+at and found the time taken to go up.

Hence time taken to come down will be 2t.In this same the car should have travelled a certain distance.Now this is where im stuck since i only have the acceleration not the speed of the car D:
 
  • #4
tiny-tim
Science Advisor
Homework Helper
25,832
251
Hey Torpedo007! :smile:
I fist used the basic V=U+at and found the time taken to go up.

Hence time taken to come down will be 2t.

(btw, you could have used V = -U and found the total time, or 0 = Ut + at2/2 :wink:)
In this same the car should have travelled a certain distance.Now this is where im stuck since i only have the acceleration not the speed of the car D:

Call the speed of the car c, put it in the x equation, and you should find it cancels at the end. :wink:
 
  • #5
Call the speed of the car c, put it in the x equation, and you should find it cancels at the end. :wink:

Sorry to be a bother but can you just elaborate a bit more please , i dont understand D:
 
  • #6
tiny-tim
Science Advisor
Homework Helper
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The boy has initial speed c0, and acceleration 1.

The ball has initial distance x = 0 and initial horizontal speed vx,0 = c0.

So when the ball lands, where is the ball, and where is the boy?
 
  • #7
The boy has initial speed c0, and acceleration 1.

The ball has initial distance x = 0 and initial horizontal speed vx,0 = c0.

So when the ball lands, where is the ball, and where is the boy?

Ah i think i finally i got it ;D thanks a load
 

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