Which of the following is true about high-energy mechanical devices?
a. they usually need to be kept warm in order to preserve mechanical energy.
b. they usually need to be cooled to dissipate thermal energy build-up and prevent damage.
c. they usually convert radiant energy into electrical energy.
d. during an energy conversion, none of the energy is transferred as thermal energy because the devices are free of friction.

acceleration = (change in speed) / (time for the change)

change in speed = (20-120)= -100 m/s.

1.5 min = 90 sec

acceleration = -100/90 = -1.11 m/s^2.

we don't care about the 150kg or the 2,500 meters. they don't make any difference.

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asthenosphere and convection

firearm identification is the process of analyzing the bullets and cartridge cases left at a crime scene to determine if they came from a particular firearm. marks on the bullets and cartridges may be common to every firearm of that type. these are called class characteristics.