00:01
Explain why, the answer to part a does not depend on the radius of the marble, and we're also asked to find the minimum height required for the marble not to fall into the pit.
00:12
Okay, so from our diagram, our vertical distance, d, is 45 minus 25, which is 20 meters.
00:22
From our equation's motion, y is equal to v -0 -t plus one -half, a -y -t -squared.
00:30
So 20 is equal to 1 1 half times 9 .8 t squared, and so our time is 2 .02 seconds.
00:40
In our horizontal direction, x is equal to vt.
00:45
So v is x over t, which is 36 over 2 .02, which is 17 .8 meters per second.
00:56
Now we can apply our conservation of energy.
00:59
Mgh is equal to 1 half mv squared plus 1 half times 2 fifths mr squared times v over r squared.
01:10
So our height is v squared over 2g...