1. You throw a 1.00 kg stone horizontally off the edge of a 10m high cliff with
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Question
1. You throw a 1.00 kg stone horizontally off the edge of a 10m high cliff with an initial velocity of 8.00 m/s. How fast is the ball moving when it hits the ground?
Answer this question first by using kinamatics, and then using energy conservation. Neglet air resistance in both cases.
2. A costumed crime fighter stands on top of a 30 m hugh building. She throws a 2.00 kg rock with an initial velocity of 20.0 m/s towards a suspected bank rober. The bank robber is standing on a neighboring building that is 38m high. How fast is the rock going when it hits the robber?
Explanation / Answer
1)
let t is the time taken to reach ground.
h = 0.5*g*t^2
t = sqrt(2*h/g)
= sqrt(2*10/9.8)
= 1.4286 s
vx = vox = 8 m/s
vy = voy + g*t
= 0 + 9.8*1.4286
= 14 m/s
v = sqrt(vx^2+vy^2)
= 16.125 m/s
2)
let m is the mass of the rock
0.5*m*v1^2 = 0.5*m*v^2 + m*g*(h2-h1)
v1^2 = v2^2 + 2*g*(h2-h2)
v2 = sqrt(v1^2 - 2*g*(h2-h1))
= sqrt(20^2 - 2*9.8*(38-30))
= 15.6 m/s
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