# physics

posted by .

(a) a spherically shaped buoy is made from wood, which has a specific gravity of 0.6. find the acceleration of the buoy when released from rest at the bottom of a freshwater lake. (b) if the buoy starts out 10 m below the surface of the water, determine the height above the water that it will rise after it shoots out of the water.

• physics -

Buoyancy = 1000 kg/m^3 * 9.81 * vol
weight = 600 kg/m^3 * 9.81 * vol

net force up = 400 * 9.81 * vol

F = m a

400 * 9.81 * vol = 600 * vol * a

a = (2/3) * 9.81
--------------------------------
work done in rise to surface
= F * 10 = 4000*9.81*vol
= Kinetic energy on exit from water
= (1/2) m v^2
= .5 * 600 * vol * v^2
so
300 v^2 = 4000* 9.81
v^2 = 130.8
v = 11.4 m/s initial speed up

Ke = Pe at stop = m g h
but oh. I did not have to do that
work done during rise = m g h directly
4000*9.81*vol = 600*vol*9.81 * h

h = (40/6) = 6 3/3 m

note g did not matter in part b

NOte also that this problem ignores the force required to accelerate the water around the sphere. This "added mass" is actually comparable to the mass of water displaced by the sphere. I bet the text writer did not even know that (hydrodymanics, not usually covered in school or college physics but very important if you are designing fishing gear)

• physics -

why is work done during the rise= mgh directly?

## Similar Questions

1. ### Physics

Archimedes principle. The weight of the bouy is given, so the weight of water displaced by the submerged part of the bouy equals that. Figure the volume that weight of water displaces, then figure the height of a .33m diameter column …
2. ### physics

A lobsterman's buoy is a solid wooden cylinder of radius r and mass M. It is weighted on one end so that it floats upright in calm sea water, having density . A passing shark tugs on the slack rope mooring the buoy to a lobster trap, …
3. ### Precalc

I am having trouble figuring out this question Jan observes a buoy bobbing up and down through a total amplitude of 8 feet. Beginning at the top of the wave, if the buoy completes a full cycle every 8 seconds, what is the height of …
4. ### Physics

You are on a boat heading out to sea. The boat is going 5m/s toward a buoy (the origin in your chosen frame of reference) that is 300 meters away. How long will it take to be 500 meters beyond the buoy?
5. ### Physics

A cylinder shaped buoy is stationary out on a lake. The height of the buoy is 1 m and the diameter is 30 cm and it‘s mass is 50 kg. Now a whale swims under the buoy and hit it. The buoy raises up and begins to oscillate. a) Find …
6. ### physics

A buoy oscillates in simple harmonic motion according to the motion of waves at sea. An observer notes that the buoy moves a total of 6 feet from its lowest point to its highest point. The buoy returns to its highest point every 15 …
7. ### physics

A buoy oscillates in simple harmonic motion according to the motion of waves at sea. An observer notes that the buoy moves a total of 6 feet from its lowest point to its highest point. The buoy returns to its highest point every 15 …
8. ### Physics

A speedboat moving at 29 m/s approaches a no-wake buoy marker 98.3 m ahead. The pilot slows the boat with a constant acceleration of -3.61 m/s2 by reducing the throttle. How long does it take the boat to reach the buoy?
9. ### Physics

A lobsterman’s buoy is a solid wooden cylinder of radius r and mass M. It is weighted at one end so that it floats upright in calm sea water, having density. A passing shark tugs on the slack rope mooring the buoy to a lobster trap, …
10. ### calculas

A buoy oscillates in simple harmonic motion y = A cos(ωt) as waves move past it. The buoy moves a total of 2.7 feet (vertically) from its low point to its high point. It returns to its high point every 18 seconds. (a) Write an …

More Similar Questions