college-kid
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Homework Statement
A boy at the top of a roller coaster falls through a vertical distance of 20m. What is the final speed of the boy if:
a) His initial speed was 0
b) His initial speed was 5 ms-1
Homework Equations
GPE at top = KE at bottom
mgh = 1/2mv^2
gh = 1/2v^2
v = √2gh
if the initial velocity (u) was not equal to zero, the maths becomes slightly different
initial total energy = final total energy
1/2mu^2 + mgh = 1/2mv^2
therefore...
v^2 = u^2 + 2gh
The Attempt at a Solution
a) 2x9.8x20 = 392
b) 5^2 + 2x9.8x20 = 417
The answers are:
a) 19.8 ms-1
b) 20.4 ms-1
What on Earth am I doing wrong... what can I do... or what? D: I just don't understand!