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Need some simple physics help.

This is embarrassing, I know. I asked all my friends and they didn't want to answer me because of how stupid this question was.. But here it goes:
Looking at this picture, there are 4 frames of the ball:
http://i.gyazo.com/b04b279d05606ace177bf3a761c61503.png
This picture was shot through a 30 frames / second camera.
How many seconds elapsed from the start to the top?
I think it's 2/15 seconds but my friend said to check my units and he sent me this:
http://www.purplemath.com/modules/fraction3.htm
-_-
I am so confused so if someone could help I would gladly appreciate it!

October 30, 2014

5 Comments • Newest first

mujura1

Wow, thanks guys! I finally got through my assignment! <3 <3

Reply October 30, 2014
SouIStrike

frame time = 1/30 sec
and the stroboscope captured 4 "images" of the ball.
so the stroboscope flashed 4 times as the ball fell through the picture? (then you are right?)

My physics teacher once suggested doing this as a project/lab/ w/e in high school. It was to demonstrate linear momentum and 2d collisions... flash a stroboscope, let billiard balls collide, and take pictures. That's one way to measure movement.. if you're interested in this stuff lol

Reply October 30, 2014
bloodIsShed

you're correct. your friends are just trolling/messing with you.

Reply October 30, 2014
Ningy

this is maths not physics, and u are correct 2/15 = 4/30 = 4 frames out of 30

no idea what ur friend is doing, u shouldnt be his friend he is influencing u to be bad at maths

Reply October 30, 2014
ShammyShakes

Using dimensional analysis:

30 frames / second is the same as second / 30 frames.

Thus, 1 second / 30 frames = x seconds / 4 frames and x should equal 2/15. Your friend is incorrect.

Reply October 30, 2014