Thank you :) Joe looks at a bird and says it is moving to the right. Shmo looks at the same bird at the same moment, but he says it is moving to the left. Which is true?

a. Joe and Shmo must be in different reference frames.
b. The bird is actually not moving at all.
c. Joe and Shmo must have the same speed and direction (This answer is incorrect)
d. One of them is right and one of them is wrong.

Aproton is projected toward a fixed nucleus of charge +ze with velocity vo. initially the two particles are very far apart. when the proton is a distance r from the nucleus its velocity has decreased to 1/2vo. how far from the nucleus will the proton be when its velocity has dropped to 1/4vo?

Acave rescue team lifts an injured spelunker directly upward and out of a sinkhole by means of a motor-driven cable. the lift is performed in three stages, each requiring a vertical distance of 10.0 m: (a) the initially stationary spelunker is accelerated to a speed of 4.90 m/s; (b) he is then lifted at the constant speed of 4.90 m/s; (c) finally he is decelerated to zero speed. how much work is done on the 68.0 kg rescue by the force lifting him during each stage?

Which of the following are appropriate acceleration units?