Physics help?

2016-08-24 7:49 am

Adolf and Ed are wearing harnesses and are hanging at rest from the ceiling by means of ropes attached to them. Face to face, they push off against one another. Adolf has a mass of 130 kg, and Ed has a mass of 75 kg. Following the push, Adolf swings upward to a height of 0.67 m above his starting point. To what height above his own starting point does Ed rise?

回答 (1)

戇戇居士

2016-08-24 8:09 am

✔ 最佳答案

Denote Adolf as "1", and Ed as "2".

Consider Adolf after the push :
Kinetic energy after the push = Potential energy of rising up
(1/2)m₁v₁² = m₁gh₁
v₁² = 2gh₁ = 2g(0.67)
v₁ = √(1.34g) m/s

Consider the push :
Total momentum after the push = Total momentum before the push
m₁v₁ + m₂v₂ = 0
130√(1.34g) + 75v₂ = 0
v₂ = -(130/75)√(1.34g) m/s

Consider Ed after the push :
Potential energy of rising up = Kinetic energy after the push
m₂gh₂ = (1/2)m₂v₂²
h₂ = (1/2)v₂²/g
h₂ = (1/2)[-(130/75)√(1.34g)]²/g
h₂ = (1/2)(130/75)²(1.34)
Height above above the starting point that Ed rises, h₂ = 2.01 m

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