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bobie
Gold Member
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Suppose a point mass B (m = 2 Kg) is rotating on a massless string (r = 2m) at v = 3m/s. Then KE = 9 J, p = 6 Kg m/s and L = p * r = 12 Nm (left in the sketch)
Suppose B collides with A (m=2) the bob of a pendulum on a massless rod r = 1m. Is L conserved? It seems that there is no external torque.
If L is conserved then the speed of A must be 12 /( 1 * 2) = 6 m/s but in this case KE is 36 J, that is 4 times greater. If E is to stay the same, as it seems obvious, v must remain 3 m/s but angular momentum will then be L = 6 * 1 = 6 Nm, that is half the original 12 Nm.
- 1) Is L conserved or there has been an external torque?
- 2) If we want to use the general formula L = I / ω , L = 12, ω = v / C = 3/ 4π → I = 12*4π/3 = 48 π/ 3 is this correct?
Thanks for your help
Suppose B collides with A (m=2) the bob of a pendulum on a massless rod r = 1m. Is L conserved? It seems that there is no external torque.
If L is conserved then the speed of A must be 12 /( 1 * 2) = 6 m/s but in this case KE is 36 J, that is 4 times greater. If E is to stay the same, as it seems obvious, v must remain 3 m/s but angular momentum will then be L = 6 * 1 = 6 Nm, that is half the original 12 Nm.
- 1) Is L conserved or there has been an external torque?
- 2) If we want to use the general formula L = I / ω , L = 12, ω = v / C = 3/ 4π → I = 12*4π/3 = 48 π/ 3 is this correct?
Thanks for your help
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