A 0.25 kg book falls off a 2 m shelf on to a 0.5 m chair. What was the change in GPE?

The equation of GPE is mgH, where m is mass, g is gravitational acceleration, and H is the height.

If we're solving for the change in GPE, then:

∆ = mg∆H

Input our given values for m and g:

∆ = 0.25 * 9.80 * ∆H

The book falls from 2 meters high to 0.5 meters high, so:

∆ = 0.25 * 9.80 * (2.0 - 0.5)

∆ = 0.25 * 9.80 * 1.5

∆ = 3.675 (J)

Adjust for significant figures:

∆ = 3.7 (J)

The change in gravitational potential energy was 3.7 (J)

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i just did this and got a 100.

it's when something is going so fast it makes a loud noise, breaking the sound barrier, for example: a jet makes a loud noise, not only cause of the jet but because they reached a point where they went so fast that you can year the noise from various parts, kinda like a police car, lets say the car was going   so fast that you hear the siren of the cop car right next to you, but the car is probably a mile a way, it's cos the siren was next to you a few seconds if you understand me