Yahoo Answers: Answers and Comments for Mechanics: Energy conservation problem with spring! Please help..? [Physics]
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From Zabedul
enUS
Sat, 16 Nov 2019 19:15:33 +0000
3
Yahoo Answers: Answers and Comments for Mechanics: Energy conservation problem with spring! Please help..? [Physics]
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https://answers.yahoo.com/question/index?qid=20191116191533AAJwqWO
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From Andrew Smith: The REASON 0.7 doesn't work is this is the...
https://answers.yahoo.com/question/index?qid=20191116191533AAJwqWO
https://answers.yahoo.com/question/index?qid=20191116191533AAJwqWO
Sat, 16 Nov 2019 21:04:50 +0000
The REASON 0.7 doesn't work is this is the distance at which the forces are in balance. ie if you put it there it would stay there. But this means it is the distance at which the system STOPS ACCELERATING. ie it is at its maximum speed at this distance.
In fact it will have gained kinetic energy and it will go EXACTLY twice this distance to come to a stop if there is no friction.
It will come to a stop when ALL of the energy has gone into the spring and nothing is moving. ie 1/2 k x^2 = mgx
x = 2 mg/k ie exactly twice the value of mg/k that you used. Incidentally at this extension the force of the spring will also be exactly twice the force of gravity on the hanging mass so it will accelerate backwards and perform SHM. But I digress.
At 65 cm find the energy from gravity and the energy in the spring
1/2 (M+m) v^2 = mgh + 1/2 k h^2 Now put in the values and solve for v

From JOHN: a) y = max extension of spring
PE lost by m₂ ...
https://answers.yahoo.com/question/index?qid=20191116191533AAJwqWO
https://answers.yahoo.com/question/index?qid=20191116191533AAJwqWO
Sat, 16 Nov 2019 20:23:57 +0000
a) y = max extension of spring
PE lost by m₂ = energy stored in spring
m₂gy = 0.5ky²
y = (m₂g)/(0.5k)
= (3.2 x 9.8)/(0.5 x 45)
= 1.4m
b) v = speed of block when x (extension) = 0.65
Energy conservation:
0.5kx² + 0.5(m₁ + m₂)v² = m₂gx
v² = (3.2 x 9.8 x 0.65 – 0.5 x 45 x 0.65²)/(0.5 x 4.8)
v = 2.1m/s.