A community of Physics Phans!

I really like physics but i dont understand it.. Can some one help me..




Why is it more difficlut to do a sit-up with your hands hedind your head than when the are out-streched in front of you?
------ I thought that the shoter the x the easer it was so i dont understand y its diffrent for a sit up?





An empty coal car coast at a certain speed along a level railroad without friction A) it begins to rain. What happens to the speed of the car? B) the rain stops, and the water gradually leaks out. What happens to the speed of the car now.
---- I was going to say that there would be less friction but since there is no friction already i got lost on what would happen.

Describe all forces acting on a child riding a horse on a merry-go-round. Which of these forces provides the centripetal acceleration of the child.
-----I know it gose up and down and around but what forces do they make.

When a "super Ball" is droped, can it rebound to a heing greater that its original heing?
----- i think the answer is no but i dont know how to prove that

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