2002 AP Exam: Lab Situation w/Density and Springs

[rvhockey]

In the laboratory, you are given a cylindrical beaker containing a fluid and you are asked to determine the density ρ of the fluid. You are to use a spring of negligible mass and unknown spring constant k attached to a stand. An irregularly shaped object of known mass m and density D(D>>ρ) hangs from the spring. You may also choose among the following items to complete the task.

1. A metric ruler
2. A stopwatch
3. String.

a)explain how you could experimentally determine the spring constant k.

b)the spring-object system is now arranged so that the object (but none of the spring) is immersed in the unknown fluid. Describe any changes that are observed in the spring-object system and explain why they occur.

c)Explain how you could experimentally determine the density of the fluid.

d)Show explicitly, using equations, how you will use your measurements to calculate the fluid density ρ. Start by identifying any symbols you use in your equations.



F_spring = -kx
density = m/V



I know you're supposed to try the problem or you won't get help, but I have absolutely no idea where to go with this one. I have never done a lab like this, and I don't want anyone to do it for me, I just need a push in the right direction.

 

[quantumdude]

You should at least try to answer a first. It's fairly obvious. Imagine haning the spring vertically and then attaching the mass to it. What happens?

 

[rvhockey]

well in that case for a you would just hang the mass from the spring, measuring the length of x before and after hanging the mass, calculate F (Mg) then divide F by x to get k. But I thought you would need at least a trial to get an accurate one?

 

[rvhockey]

how about the rest of the problem? still lost