Rachel drops a ball from a hot–air balloon while her friend Lisa is watching her from the ground. Which statement about the ball's motion is true from Lisa's point of view? Assume that there is no air resistance and the hot–air balloon is moving horizontally.

A. The ball drops to the ground along a straight–line path.

B. When the ball lands, the hot–air balloon will be ahead of it.

C. When the ball lands, the hot–air balloon will be behind it.

D. When the ball lands, the hot–air balloon will be directly above it.

What is work? how much work is done to move an object 0 meters?

Aball horizontally thrown from a cliff at 8m/s

Uranium has two naturally occurring isotopes. 238u has a natural abundance of 99.3% and 235u has an abundance of 0.7%. it is the rarer 235u that is needed for nuclear reactors. the isotopes are separated by forming uranium hexafluoride uf6, which is a gas, then allowing it to diffuse through a series of porous membranes. 235uf6 has a slightly larger rms speed than 238uf6 and diffuses slightly faster. many repetitions of this procedure gradually separate the two isotopes. what is the ratio of the rms speed of 235uf6 to that of 238uf6? express your answer to five significant figures.