1. A person throws three identical rocks off a cliff of height h with exactly the same speed v0 each time. Rock A is thrown vertically upward, rock B is thrown straight out horizontally, and rock C is thrown straight downward. If we ignore the effects of air resistance, which rock hits the ground with the greatest speed?
a. Rock A
b. Rock B
c. Rock C
d. All rocks hit with the same speed.
2. Consider a ball interacting gravitationally with the earth. Imagine that we choose to define the interaction's potential energy to be zero if the ball is at ground level. A person standing at the bottom of a well throws the ball vertically upward from 20 m below the ground level. The ball makes it all the way up to 1 m below ground level before falling back into the well. The total energy of the ball-earth system is
a. Positive (in this particular case)
b. Positive (because total energy is always positive)
e. The answer depends on the rock's mass
The Attempt at a Solution
1. Is it (a), because rock a gets the most time for gravity to accelerate it? Or do all the rocks reach a terminal velocity (but is there terminal velocity without air friction?)?
2. I think that the answer is (d) Negative, because if V(z) = mgz and z < 0, then whatever the mass of the rock is, the potential energy would be zero. But if it asks for the TOTAL energy, do I also include its kinetic energy? In that case, would the TOTAL energy still be negative?
Thanks for the help guys. This forum has helped me a lot as I am taking an introductory physics class, which has a professor who doesn't teach and a textbook that doesn't explain (Six Ideas that Shaped Physics).