A heavyweight boxer winds up and punches a punching bag. Which of the following are true? (Choose 2) A The punching bag exerts more force than the fist.
B The fist exerts more force than the punching bag.
The force acting on the bag is equal and opposite to the force acting on the fist.
D
The fist creates the action force and the punching bag creates the reaction force.
E There is no force between the two objects because they are balanced.

Mechanical energy is when the amount of kinetic and potential energies added together remains the same. conserved created lost

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?

Point charges q1=+2.00μc and q2=−2.00μc are placed at adjacent corners of a square for which the length of each side is 1.50 cm . point a is at the center of the square, and point b is at the empty corner closest to q2. take the electric potential to be zero at a distance far from both charges. part a what is the electric potential at point a due to q1 and q2? express your answer with the appropriate units.