# Number of elastics needed to safely fall

1. Oct 31, 2013

1. The problem statement, all variables and given/known data Hi, I have this assignment that is killing me trying to figure out. I'm in grade 11 physics.

Basically, the teacher will be dropping an object at a certain height (We do not know yet). The object will be attacked to the place where it was dropped with elastic bands. We have to figure out how many elastic bands to attach to each-other to get as close to the floor as possible without hitting it.

I wasn't sure what I would need concerning data, so what I did was drop a 20g mass with 1 elastic from a certain height and saw how far it fell. I then repeated this with 100g and 200g. I repeated this whole procedure with 2 elastics, 3 elastics, and 4 elastics.

I believe the teacher will be dropping it from the ceiling. On the day of the dropping, she will give us the mass of the object to be dropped and the height it will be dropped from. We must predict how many elastics are needed to drop the object as far as possible without hitting the floor.

2. Relevant equations

This is in our energy unit, and these are the formulas we have learnt so far:

W=Fd
eg=mgh
ek=1/2mv^2
em=eg+ek

3. The attempt at a solution

I tried getting the Potential Energy by using one of the masses, gravity and the height it fell.

I also tried finding a way to do this with kinematics, but to no avail...

Not really sure where to go with this...

2. Oct 31, 2013

### Simon Bridge

That's a good method.
You want to work out the relationship between the distance your test mass fell and the number of elastics used.
Since you don't know what the object is yet either, then you also need the relationship between the distance fallen and the weight of the test mass.

Make a graph of your data and see if you can see any patterns?

The equations may be able to help you too ... i.e. is 1 elastic band stores mgh of energy, then two elastic bands will absorb how much? Use your graphs to check your assumptions.