Conservation of Momentum (Ch 7-9, Q6)

[gcombina]

Homework Statement

A stationary bomb explodes in space breaking into a number of small fragments. At the location of the explosion, the net force due to gravity is zero Newtons. Which one of the following statements concerning this event is true?
(a) Kinetic energy is conserved in this process.

(b) The fragments must have equal kinetic energies.

(c) The sum of the kinetic energies of the fragments must be zero.

(d) The vector sum of the linear momenta of the fragments must be zero.

(e) The velocity of anyone fragment must be equal to the velocity of any other fragment.

Homework Equations

Conservation of Momentum
(mv) before = mv (after)

The Attempt at a Solution

(a) Kinetic energy is conserved in this process.
This is a NO, because Kinetic energy isn't conserved, the energy is lost
(b) The fragments must have equal kinetic energies
I assume the fragments do not longer have Kinetic energy but Potential energy so its a NO
(c) The sum of the kinetic energies of the fragments must be zero.
Fragments do not longer have Kinetic energy as they are stationary, they have potential energy (I have no clue if this reasoning is correct) so the answer is NO
(d) The vector sum of the linear momenta of the fragments must be zero.
mass and velocity = 0 so Yes
(e) The velocity of anyone fragment must be equal to the velocity of any other fragment.
The velocity is ZERO so they all have the same velocity so the answer is YES to this too (Is this correct? like some fragments can be having a velocity of 0 and others can have some movement still)

 

[gneill]

You need to rethink what is going on here. Before the bomb explodes it is sitting stationary, so no kinetic energy. After it explodes, whatever energy powers the bomb (chemical, atomic,...) is turned into heat and kinetic energy of the fragments. The fragments scatter in all directions. Because the explosion takes place in space far from any large gravitational forces and without any friction to slow anything down, the fragments will all continue to travel indefinitely along straight paths.

 

[gcombina]

I see, that is why they said 0 gravity...brb