How to find speed ?

Question

During the Grammy awards, Pink stunned the audience with some acrobatics. She was hoisted about 20m above stage with silk ropes ( all the while she was singing ). How much potential energy did she gain during this hoist? If her hoists had broken at the highest point what would be her speed as she hits the stage? Assume pink weighs 70kg.

I ok know how to calculate potential energy but I don't know how to find the speed as she hits the stage . Can you show detailed steps please. I tried solving and I got 20 m/s but have no idea if it's right

Answer 1

During the Grammy awards, Pink stunned the audience with some acrobatics. She was hoisted about 20m above stage with silk ropes ( all the while she was singing ). How much potential energy did she gain during this hoist? If her hoists had broken at the highest point what would be her speed as she hits the stage? Assume pink weighs 70kg.

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It's very nice you can calculate potential energy (with respect to stage effect):

it must be,

                      mgh , with h=20m

 

let's have a little break here:

the singer can't move her center of inertia (herself, that is) alone using her internal energy (muscles). All the physical changes in vertical direction (up-down) happens just due to gravitational interactions.

Thus, her speed, as she hitting the stage, is defined by her kinetic energy, which, in its turn, converted from potential energy:

That is,

                  mgh=mV^2/2

 

you define V from here. (see, mass isn't relevant)

Now, what is "h" here - it must be less than 20m - she can't hit the stage "with her center of inerti" - you can imagine that.

With this accuracy, the problem solved.

 

Good luck:)

 

P.S. concentrate you n=mind in physical scenario ... mass, Pink, ropes, stage ... so many "deflecting" information ...