- #36
PeterO
Homework Helper
- 2,442
- 67
flyingpig said:[PLAIN]http://img820.imageshack.us/img820/8761/fallingblockonspring.gif[/QUOTE]
The diagram was perfect BEFORE you wrote your d on it!
Go back to square one here.
Imagine you are going to perform the following experiment.
You are going to place the spring, normally found in the suspension of a car, on the floor. You are then going to drop a brick, from shoulder height, onto the spring.
That is what the problem is all about.
If I knew how tall you were, and how long the original spring was, I would be able to calculate exactly how fast the brick was traveling when it first contacted the spring. HOWEVER, I don't need those distances as I was already told the brick was traveling at speed v when it reached the spring - the calculation had already been done for me!
SO we only calculate from there on.
When the brick is finally stopped by the spring, it has traveled a further distance d.
It has lost mgd of potential energy since first contacting the spring. It has also lost all its kinetic energy: ½mv²
All that energy has been stored in the spring by compressing it an amount d.
SO
½kd² = mgd + ½mv²
re-arrange and solve for m.
Now the original question involved dropping something onto a spring, but I forget what, so I called it a brick.
NOTE: the object was DROPPED onto a spring, not placed on top of the spring.Peter
½ ⋅ ²
Last edited by a moderator: