Question

Conservation of Mechanical Energy:
A pendulum bob is released from some initial height such that the speed of the bob at the bottom of the swing is 1.9m/s. What is the initial height of the bob?

Answer 1

Why would K(A) be 0?

Answer 2

Yes, it 'released' without initial speed right?

Answer 3

isnt the initial speed 1.9 m/s?

Answer 4

No, that's the speed at B.

Answer 5

oh ok so you got the zero from A?

Answer 6

Yup :)

Answer 7

but the book says tha answer is 0.18m but how would you get that answer?

Answer 8

*the

Answer 9

I got the same answer. I wrote the formula at the picture:\[h=\frac{v^2}{2g}\]

Answer 10

when it comes to a pendulum does it not depend on the lenght of the string?

Answer 11

U=mgl

Answer 12

ok, so you would use that formula, h=v^2/2g to get 0.18m?

Answer 13

@Jasminebunnies : Yes

Answer 14

ohhh ok and the zero is put there because there is no mass?

Answer 15

Omg! (^ ^!)
Which zero?

Answer 16

lol! the zero in your original equation that you said came from A, in front of mgh

Answer 17

That's because v=0 at highest point.

Answer 18

ohhh ok, is that because it has not been released at that point?

Answer 19

@imron07

Answer 20

Because by the time the pendulum is released, the velocity is zero. It start from rest.

Answer 21

yes, ok! thank you! I understand now :)

Answer 22

ok ;)