Can a chemical change be undone?

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?

Calculate a pendulums frequency of oscillation (in hz) if the pendulum completes one cycle in 0.5s.

Four 5-gram blocks of metal are sitting out in the sun and absorb the same amount of heat energy. use the following specific heat capacity data to determine which block will increase its temperature the most.