How much centripetal force is needed to make a body of mass 0.5kg to move in a circle of radius 50cm with speed 3ms^-1 ?

The percent efficiency of a machine can never be 100% (or greater), because in the real world some energy is always converted into a. heat b. work c. input force d. output force

Name three different units of energy used to measure heat and describe what type of situations each is usually used.

Light from the sun reaches the earth in 8.3 minutes. the velocity is 3.00 x 10^8 m/s. how far is earth from the sun? i know how to get to d = (3 x 10^8 m/s)(498 sec). i just don't know how to get from there to the answer being 1.5 x 10^11 m.