# Mass of a comet problem

[SOLVED] Mass of a comet problem

On July 4, 2005, the NASA spacecraft Deep Impact fired a projectile onto the surface of Comet Tempel 1. This comet is about 9.0 {\rm km} across. Observations of surface debris released by the impact showed that dust with a speed as low as 1.0 {\rm m/s} was able to escape the comet.

1)Assuming a spherical shape, what is the mass of this comet? ( The escape speed for an object at the surface of Earth is 11.2 {\rm km/s} ).

2)How far from the comet's center will this debris be when it has lost 70 {\rm \%} of its initial kinetic energy at the surface?

I have absolutely no idea what to do. any help would be appreciated.

Related Introductory Physics Homework Help News on Phys.org
and here is the link if you are confused.

http://session.masteringphysics.com/myct/problemWork?template=problemView&assignmentProblemID=2736711 [Broken]

Last edited by a moderator:
berkeman
Mentor
Thread moved to Homework Help forums. Joe, start by telling us about the term "escape velocity", and how it relates to gravitational attraction.

the only thing i know is that the escape velocity for the earth is equal to the square root of (G*mass of earth/radius of earth). our teacher really doesnt explain anything.

maybe i could use that and compare it to the escape velocity of the comet somehow but i don't know how. its just a really confusing problem because not much is explained.

berkeman
Mentor
Here's a reference on escape velocity. This should give you all that you need to solve the question. Read through this, and then post your work here if you still need help.

http://en.wikipedia.org/wiki/Escape_velocity

ok. solving for M =v^2*r/(2G) and plugging in i got 3.37 x 10^13. does that sound about right?

berkeman
Mentor
What are your units? What did you get for part B) ?

my units are in kg.

thanks i got it.

bump, I have no idea how to get part b

berkeman
Mentor
bump, I have no idea how to get part b
What did you get for the answer for the first part? What can you tell us about the relationship between KE, PE, and total energy?