I need help for an easy Physics Question
I know everyone will think I'm dumb because I can't even answer this simple Physics Question, but can I still get some help as to how to answer it? Please, I would really appreciate it. Here is the question:
[b]If you drop a coin from a height of 9.5m, how fast will it be traveling when it reaches the ground?[/b]
Somehow on the answer sheet it says 13.7m/s, but I don't even know how to get this answer. Shouldn't you have to multiply gravity by the height to get the velocity? That equals -93.1m/s, but that can't be the right answer.
July 25, 2012
11 Comments • Newest first
remember that it is possible to have negative answers (even though your answer is indeed incorrect); because the numbers are based on how you set up your coordinate system.
Assuming g=9.8m/s, and neglecting air resistance:
Delta y = uyt + 1/2ay(t^2) -> (9.5) = 0t + 1/2(9.8)(t^2) -> t = 1.39s
v = u + at -> v = (0) + (9.8)(1.39) -> v = 13.6m/s
EDIT: Just read the previous comments, UglierBetty has the best answer. I forgot about that formula. Also, noticed I wasted a couple mins typing this up.
Don't think you're dumb. Even the people above weren't 100% sure when they answered.
@darkwizard27: Mhm.
I just tend to stay away from equations like that because there are so many more versions of it.
[quote=UglierBetty]Mass cancels in a conservation of energy scenario.
And your method has more complicated algebra.[/quote]
Oops, forgot
It simplifies into the same equation as yours though, considering v_initial is 0.
[quote=darkwizard27]You can't use conversation of energy unless you know the mass of the coin. Use v_final^2 = v_initial^2 + 2gh instead.[/quote]
Mass cancels in a conservation of energy scenario.
And your method has more complicated algebra.
You can't use conversation of energy unless you know the mass of the coin. Use v_final^2 = v_initial^2 + 2gh instead.
@school239: No problem! And I like answering your questions on here!
I see you've learned about conservation of energy now? See how much easier it makes things?
[quote=UglierBetty]omg you and physics questions!
OT: 9.5(9.8)=(0.5)v^2
Solve for v[/quote]
Thanks a lot, I know my questions may seem annoying to you but as you can tell I'm uber dumb and I have no idea where else to find the answer since basil is such a nice community.
Don't think of gravity as gravity, think of gravity as acceleration. That'll clear up the minus sign.
Find out how long it takes for the coin to drop 9.5 meters. Then multiply that time by gravity to find the velocity.
omg you and physics questions!
OT: 9.5(9.8)=(0.5)v^2
Solve for v