# (Movement Homework) What is the speed of a marble falling on the moon?

• sigurdfromnor
In summary, the conversation discusses a problem in physics involving a marble attached to a string and an astronaut on the moon. The person is struggling to find the correct formula to use and asks for pointers. The conversation then suggests thinking of the problem in terms of kinetic and potential energy, and provides guidance on how to approach the problem.

#### sigurdfromnor

Homework Statement
An astronaut on the moon has a string with a marble attached to the end.

he pulls the string [straight out] to the side and releases it [the marble]. the marble falls down and continues upwards on the other side until it reaches the same hight as it was when the astronaut released it .

assume that the string has a mass so small that we look away from it.
the marble weighs 10g and the field strength of the moon is gm = 1.6N / kg ,
the distance from the marbels highest point to its lowest is 1M.

what is the speed of the marble when it is at its lowest point ?
Relevant Equations
N/A
Sorry for the bad english.
This might sound stupid but I am pretty new the physics and i can't seem to find what formula to use on this problem when only the mass, gravity and height of the fall is given.
and i can't find a similar problem in the book, could someone give me any pointers?
Thanks

[Additions in brackets by a Mentor to clarify the problem a bit]

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What book are you using? Could you solve it if it were on Earth instead of the Moon?

im studying in norway so the book is in norwegian, It's called (Rom Stoff Tid) that probably dosen't help you hahah.
No i wouldn't be able to solve it on earth,
if i got a starting speed i could probably solve it, but since it from a stand still I am not sure what equation to use.
im pretty new to physics, so I'm still learning the basics.

You should be able to find similar problems. You can think of this (if I understand you) as a simple pendulum.

Hint: Have you covered any conservation laws?

berkeman
sigurdfromnor said:
Homework Statement:: An astronaut on the moon has a string with a marble attached to the end.

he pulls the string to the side and releases it. the marble falls down and continues upwards on the other side until it reaches the same hight as it was when the astronaut released it .

assume that the string has a mass so small that we look away from it.
the marble weighs 10g and the field strength of the moon is gm = 1.6N / kg ,
the distance from the marbels highest point to its lowest is 1M.

what is the speed of the marble when it is at its lowest point ?
Relevant Equations:: N/A

Sorry for the bad english.
This might sound stupid but I am pretty new the physics and i can't seem to find what formula to use on this problem when only the mass, gravity and height of the fall is given.
and i can't find a similar problem in the book, could someone give me any pointers?
Thanks
I guess this is what is often called a pendulum!

sigurdfromnor said:
if i got a starting speed i could probably solve it, but since it from a stand still
So you do have the starting speed. A stand still means zero starting speed.

A way to think of this problem, is in terms of gravitational potential energy and kinetic energy.
1) Do you know what is the formula for kinetic energy and gravitational potential energy?
2) Where do these energies are maximum or minimum, calculate these energies for points A and B.
3) Finally, what would only be left is to realize that the gravitational potential energy must have been entirely converted into kinetic energy.

sigurdfromnor
phystro said:
A way to think of this problem, is in terms of gravitational potential energy and kinetic energy.
1) Do you know what is the formula for kinetic energy and gravitational potential energy?
2) Where do these energies are maximum or minimum, calculate these energies for points A and B.
3) Finally, what would only be left is to realize that the gravitational potential energy must have been entirely converted into kinetic energy.
Thanks, this helped a lot. I was finally able to solve it. :)

berkeman