# Homework Help: Stuck on physics problems

1. Sep 1, 2004

### lmf22

I'm having trouble figuring these 2 problems out:

4000cm^3 (.004m^3) of oil is spilled onto a smooth lake. If the oil spreads out uniformly until it makes an oil slick 3 molecules thick, with adjecent modlecules just touching, estimate the diameter of oil slick. Assume the oil molecues have diameter of 2x10^-10.

The other problem is:
A bowling ball traveling with constant speed hits the pins at the end of a bowling land 16.5m long. The bowler heas the sound of the ball hitting the pins 2.70 seconds after the ball is released form his hands. What is the speed of the ball? The speed of sound is 340m/s.

Any hints on how to get started would be greatly appreciated.

2. Sep 1, 2004

### needhelpperson

For "the other problem":

You know that t(ball) + t(sound) = 2.7 seconds

so you can set up the equation as

16.5= 340t(sound)

after that you know the t(ball) which is really easy to solve from there...

3. Sep 1, 2004

### suffian

In the first problem, if the oil "spreads out uniformly", I would take that to mean at it looks like a disc when viewed from above. The volume of this thin disk is the area of the disc multiplied by the height. Your trying to solve for the diameter (more or less radius).. see if that gets you started.

In the second problem, split it up into two phases. One, when the ball goes from bowler to pin, and two, when the sound of the crash goes from pin to bowler. The two are lated by the fact that the total time it takes for both events is given.

4. Sep 1, 2004

### needhelpperson

for this problem, i assume you can treat the lake as a cylinder?
volume = .004m^3

We know the height equals 3 molecules thick so you can figure that out.

pi*r^2*h = .004m^3

just solve for r and multiply it by 2 to give the diameter.