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4. A pendulum bob of mass `1.5 kg`, swings from a height `A` to the bottom of its arc at `B`. The velocity of the bob at `B` is `4.0\ m//s`. Calculate the height `A` from which the bob was released. Ignore the effects of air friction.
4. A pendulum bob of mass 1.5 kg, swings from a height A to the bottom of its arc at B. The velocity of the bob at B is 4.0\ m//s. Calculate the height A from which the bob was released. Ignore the effects of air friction.  `KE + PE = constant`
`h = 0.80\ m`
Given:
`v_B = 4.0 m//s`
Equations
`KE + PE = constant`
Solution:
`KE_A + PE_A = KE_B + PE_B`
`0 + mgh = 1/2mv_B^2 + 0`
`h = v_B^2/(2g)`
`h = (4.0 m//s)^2/(2 times 10\ m//s^2)`
`h = 0.80\ m`
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