Concept of Force Confusion

  • Thread starter mrlucky0
  • Start date
  • #1
mrlucky0
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1

Homework Statement



Object A and B are placed on a spring. Object A has twice as much mass as object B. If the spring is depressed and released, propelling the objects into air, object A will:

answer: rise to the same height as object B

Homework Equations





The Attempt at a Solution



Based on my reasoning and math, I am confused why both objects would rise to the same height:

The force on both objects is the same, F. And 2*mass of B = mass of A

F = (mass of A)*(accl. A) = (mass of B)*(accl. B)
F = 2*(mass of B)*(accl. A) = (mass of B)*(accl. B)

cancel out (mass of B):
F = 2*(accl. A) = (accl. B)

Since the upward acceleration of B is twice the that of A, why would the height be the same?
 

Answers and Replies

  • #2
tyco05
161
0
I've only briefly thought about your attempt:

You are only considering the upward forces due to the spring.

What about the force on each object due to gravity... will it be the same?

Consider...
 
Last edited:
  • #3
HallsofIvy
Science Advisor
Homework Helper
43,021
971
I think the simplest way to do this problem is to use "conservation of energy". The spring has a specific amount of energy stored in it when compressed and, on release gives the same energy to A and B. They will rise to heights that give the same potential energy to both.
 
  • #4
get_physical
85
0
any one know how to approach this problem?
 
  • #5
Dadface
2,495
105
As the spring moves up A and B are pushed up with at all times equal speeds and their speeds are also equal when they lose contact with the spring.Take it from there.
 

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