A. The object is made of stone or metal, which always sink.
B. The force of gravity is stronger than the buoyant force.
C. The buoyant force is stronger than the force of gravity.
D. The mass of the item is greater than its gravity
The answer is C
By conducting exhaustive, high-intensity online research for about 15 seconds, I found a source that says the speed of sound in copper is 4600 m/s. (You could easily have completed the same research project in about 1/3 of the time it took you to type and post the question here.)
Time it takes = (distance) / (speed)
Time = (25,000 meters) / (4600 m/s)
Time = (25 / 4.6) km-sec/km
<em>Time = 5.43 seconds </em>
If something is going down a hill it can help slow it down
it can stop you from flying off a rollercoaster
<span>The mechanical energy is conserved.
I hope this helps, good luck! :)</span>
Efficiency is calculated through dividing the actual mechanical advantage by the hypothetical mechanical advantage:
- the actual mechanical advantage is 9J because that's how much work the light bulb doing
- the hypo. mechanical advantage is 100J. Ideally, in a perfect world, the light bulb can convert 100J input into 100J output, but do to resistance and other factors it is not possible.

change the decimal to a percentage:

the light bulb had 9% efficiency