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Physics help please PHYSICS?
Physics help physics stuck?
A stone is thrown vertically upward with a speed of 13.0 m/s from the edge of a cliff 65.0 m high.
(a) How much later does it reach the bottom of the cliff?
_______ s
(b) What is its speed just before hitting?
_______ m/s
(c) What total distance did it travel?
______ m
1 Answer
- RichardLv 79 years agoFavorite Answer
Acceleration due to gravity = 10 m/s^2 approximately.
a)
s = ut + 0.5at^2
65 = -13t + 5t^2
5t^2 - 13t - 65 = 0
t = (13 +/- root (169 + 4 * 5 * 65)) / 10
= 1.3 +/- 3.83275
= 5.13275 s
There is a negative answer which I will ignore. It corresponds to the stone being thrown from the bottom of the cliff so that it is travelling upward at 13.0 m/s at the top of the cliff.
b)
v = u + at
= -13 + 10 * 5.13275
= 51.3275 - 13
= 38.3275 m/s
c)
v^2 = u^2 + 2as
13^2 = 2 * 10s
s = 169/20
= 8.45 m
This is the maximum height above the top of the cliff.
Total distance = 2 * 8.45 + 65
= 81.9 m
