Question

A child is on a swing. Her mom pushes her to a height of 1.5 m above the starting position. Determine the child's maximum velocity during the swing.

Answer 1

For this question, I am supposed to fine the kinetic energy, not potential gravitation energy right? Because the Kinetic energy formula has velocity so I can find the max velocity?

Answer 2

With the information given, it is asking me to find kinetic energu right? so I then can find the velocity from the formula E(kin) = 1/2mv^2

Answer 3

mgΔd=1/2mv^2

Answer 4

then mass cancels out and I can solve for velocity

Answer 5

would it be possible to get the right answer by finding potential gravitational energy?

Answer 6

hmm ... use conservation of energy
KE = PE

Answer 7

mgh = 1/2 mv^2
v = sqrt(2*g*h)

Answer 8

is it always true for KE = PE ?

Answer 9

what about pendulum when it reaches max height. at that point it mas max potential grav energy but no kinetic

Answer 10

yep ... if you ignore dissipative forces like friction.

Answer 11

yes for the other question too.

Answer 12

how?

Answer 13

KE = 0
GE > 0

Answer 14

PE > 0

Answer 15

can you explain further?

Answer 16

hmm ... you mean why it should always be true? that KE = PE ??

Answer 17

Yea because on the pendulum when the mass reaches max height, there is an instaneous pause which means there is no kinetic energy but there still is potential energy

Answer 18

so in that case the KE is not equal to PE

Answer 19

do you know about conservation of energy?

Answer 20

yea energy is never lost

Answer 21

yep ...that's why!!

Answer 22

ok i think i understand now

Answer 23

the kinetic energy turns into potential energy but total mechanical energy is the same

Answer 24

thanks for your help

Answer 25

yep :D