If a tunnel is dug by some people along the diameter of earth and then a ball is thrown through it starting from North Pole to South Pole whether it

A) stops at center

B) comes to the other pole and stop

C) goes out of tunnel.

D) it just moves up and down.


Assuming that only gravity acts on the ball, it would arrive at the South Pole with the same velocity as it had in the beginning, so if the ball was thrown, it had $v_{i} \neq 0$ which means that $v_{f} \neq 0$. So C is the correct answer.

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    $\begingroup$ I don't know why this is down-voted. Whiile there isn't much explanation as to why this is the correct answer. It is correct. But it won't keep going "out." It will eventually stop and fall back toward the hole. All this is assuming a spherical, angularly-uniform earth where the density is only radially dependent. $\endgroup$ – Bill N Mar 26 '16 at 14:59
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    $\begingroup$ @BillN: my guess is that since it's an answer to a lazy homework question (which we discourage) the downvote is a sign to not answer it. $\endgroup$ – Kyle Kanos Mar 26 '16 at 15:06
  • $\begingroup$ @BillN Well it does depend on the initial velocity, if it will continue going "out" or fall back. $\endgroup$ – George Mar 26 '16 at 17:01
  • $\begingroup$ @Kyle Kanos Oh, I wasn't aware of that. $\endgroup$ – George Mar 26 '16 at 17:01
  • $\begingroup$ I doubt that someone could throw the ball with Earth's escape velocity. It will eventually stop and turn around, just as if you threw the ball upward. $\endgroup$ – Bill N Mar 26 '16 at 17:57

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