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Stored spring energy 
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#1
Apr2210, 11:06 AM

P: 201

Hi  Would someone check my method here please?
Thank you 1. The problem statement, all variables and given/known data Two trolleys A and B, of mass 0.70kg and 0.80kg respectively, are on a horizontal track and held together by a compressed spring. When the spring is released the trolleys separate freely and A moves to the left with an initial velocity of 4.0m/s. Calculate: a) the initial velocity of A b) the energy initially stored in the spring 2. Relevant equations F=ma 3. The attempt at a solution a) (0.70x4.0)=(0.80xV) v=(0.70x4.0)/(0.80) v=3.5m/s b) This is a transfer of elastic potential energy to kinetic energy  Energy=1/2mv^2 mv=p(momentum) 1/2(0.70x4.0)^2 + 1/2(0.80x3.5)^2 =0.0392 + 3.92 =3.9592 J 


#2
Apr2210, 11:34 AM

Mentor
P: 41,319

KE = 1/2mv^2, but you calculated 1/2(mv)^2. Not the same! 


#3
Apr2210, 11:40 AM

P: 201

ahh of course:
silly boy! (1/2x0.7x4.0^2) + (1/2x0.8x3.5^2) = 10.5 J 


#5
Apr2210, 12:44 PM

P: 201

Thanks Doc



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