Question

1. A 40.0 kg child sits on a swing 50.0 cm above the ground. Her mother pushes her to a height of 1.2 m above the ground. What is the maximum speed of the girl on the swing?

Answer 1

to me, potential energy = kinetic energy
(1/2)mgh = (1/2) mv^2
v^2 = gh
and h = 1.2m - 0.5m = 1.15 m
take square root to get v

Answer 2

why does height = 1.2 - 0.5

Answer 3

I was using the longer formula where
Kinetic Energy Initial + Potential Energly Initial = Kin Energy FINal + Pot Energy Final

Answer 4

because originally, the child is at 0.5m above the ground, not on the ground

Answer 5

the same,

Answer 6

no that way I get a negative number and I cant root it

Answer 7

I get root of -13.72 but that is not possible

Answer 8

before moving, the potential energy =0 (didn't move yet)
after moving, the kinetic energy =0

Answer 9

the negative sign show that it is upward, no meaning for the value.

Answer 10

are you sure?

Answer 11

I think so.

Answer 12

can you explain @amistre64

Answer 13

Why is there a negative value?

Answer 14

the question is ambiguous

Answer 15

what do you mean?

Answer 16

i mean, what time intervals are involved? when do we start calculating the speed? is the mothers pushing with all her strength or is this just getting her up to a certain height and letting go?

Answer 17

The question is all that is given, btw this is grade 11 physics

Answer 18

then we can prolly assume that the girl is pushed to a given height and let go an dallowed to jsut fall along the arced path.

Answer 19

Its sort of like a pendulum

Answer 20

at the bottom of the swings arc, all of the stored energy from being lifted to a given height is used, and we are in full kinetic mode

Answer 21

assuming no loss of energy: K = P at the bottom of the arc, so it must be equal to the full potential to start with, and K = 1/2 mv^2 as pointed out