- #1
Killic
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Homework Statement
A 200 kg boulder falls from rest off a 120.0 m high cliff. If the boulder experiences a frictional force of 280 N as it falls, what would be the velocity just before it hits the ground?
Homework Equations
kinetic energy = (1/2)mv2
gravitational potential energy = mgh
work = (net force)(Δd)
The Attempt at a Solution
Total force = mgh = 200kg*9.8N/kg*120m = 235200 J
Wfriction = FΔd
Wfriction = 280 N*120 m
Wfriction = 33600 J
total energy = kinetic energy + work done by friction
kinetic energy = 235200 J - 33600 J
kinetic energy = 201600 J
201600 J = (1/2)mv2
v = 45 m/s
However, according to my teacher, this answer is incorrect.