The discussion focuses on calculating kinetic and potential energy for a 55kg mass projected vertically at an initial speed of 30 m/s. The original kinetic energy is calculated using the formula W = mv²/2, yielding 24,750 Joules. The kinetic energy after 4.5 seconds requires reevaluation of the velocity due to negative acceleration, leading to the use of conservation of energy principles to find the change in gravitational potential energy. The final approach emphasizes that height does not need to be calculated directly, as energy conservation provides the necessary relationship between kinetic and potential energy.
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This is correct.physics(L)10 said:a) Original =(55)(30)2/2
This is not correct. Rethink how to calculate the speed; it's not equal to gt. (It's slowing down, for one thing. The acceleration is negative.)b) W=(m/2)(gt)2
=(55/2)[(9.8)(4.5)]2
Good. (I assume you mean v2 = ..., not 0 = ...)physics(L)10 said:ok I think I know,
v2=v1 -at
0=55-(9.8)(4.5)
You need the answer to b to get c. (You aren't given the height.)And how about c? you didn't comment on that
Not exactly. Use conservation of energy like this:physics(L)10 said:Yes my bad. and for c, does it look something like this?:
mgh=mv2/2
Those would be the speeds, from which you'd calculate KE1 and KE2 and then the difference.physics(L)10 said:So let's say, initial speed = 55 and final = 25. These would be the only differences in KE1,KE2?
You do not need the height difference. They ask for the change in PE, which can be found using conservation of energy.physics(L)10 said:How would you find out the height difference to find the potential energy difference?
I think you mean -ΔKE = ΔPE. Sure that will work--that's equivalent to the equation I gave in post #6.physics(L)10 said:Would this work? I find change in KE which then can be used in the equation -KE=PE?