1. A 40 kg rock falls from rest from the top of a 64 m high tower and falls with negligible air resistance. How much kinetic energy (KE) and potential energy (PE) does the rock have when it is 28 m above the ground?
(A) KE = 0; PE = 2.5 x 104

J (B) KE = 1.1 x 104 J; PE = 1.4 x 104

J (C) KE = 1.4 x 104 J; PE = 1.1 x 104

J (D) KE = 2.5 x 104 J; PE = 0

An astronaut in space cannot use a scale or balance to weigh objects because there is no gravity. but she does have devices to measure distance and time accurately. she knows her own mass is 77.4 kg , but she is unsure of the mass of a large gas canister in the airless rocket. when this canister is approaching her at 3.50 m/s , she pushes against it, which slows it down to 1.30 m/s (but does not reverse it) and gives her a speed of 2.60 m/s . what is the mass of the canister?