Homework Help: Physics

Posted by Jessica on Thursday, July 12, 2012 at 1:33pm.

Jack Sparrow swings on a 3 m long rope that was horizontal before he jumped from the boom of the Black Pearl. At the very bottom of his arc, he grabs Elizabeth Swann and they swing upward together. Sparrow (Depp) has a mass of 75 kg, and Swann (Knightley) has a mass of 50 kg (amazing what you can find with Google). How high do they swing after the ‘collision’?

Physics - Elena, Thursday, July 12, 2012 at 1:52pm
m1=75 kg, m2 =50 kg. L=h=3m

Law of conservation of energy
PE1=KE1
m1•g•h = m1•v1²/2,
v1=sqrt(2•g•h) =sqrt(2•9.8•3)=7.67 m/s.
Law of conservation of momentum
m1•v1 =(m1+m2) •u
u= m1•v1/(m1+m2) =75•7.67/125 =4.6 m/s.
Law of conservation of energy
KE2=PE2
(m1+m2)•u²/2=(m1+m2)•g•H,
H= u²/2g=4.6²/2•9.8=1.08 m.

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