A beam of length 5 m and mass 40 kg is placed on top of two posts: the first post is under the left end of the beam and the second post is 3 m to the right from the first post. A child with mass 20 kg starts walking along the beam from left to right. How close can he get to the right end of the beam without falling over

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?