A couple of Physics questions: An object’s momentum is dependent on its?

1. An object’s momentum is dependent on its:
A. mass and acceleration
B. energy and velocity
C. height and force
D. space and time
E. None of the Above

**I’m confused here because the formula for momentum is mass * velocity.  But in letter A, it’s mass and acceleration.  I am unsure if velocity and acceleration is pretty much the same in this case.

2. An object that floats in a fluid is ________.
A. lighter than the fluid
B. more dense than the fluid
C. heavier than the fluid
D. less dense than the fluid
E. None of the Above

3. A swinging pendulum can convert potential energy to kinetic energy and vice versa as it moves, but it will eventually stop.  
What has happened to the kinetic and potential energy then?
A. It has all been converted to chemical potential energy.
B. The two have combined and cancelled out each other.
C. It has all been converted to heat.
D. There was no outside force exerted, so the pendulum stopped due to inertia, transferring energy to the outside
E. None of the above

**Did they cancel out each other or what?

4. Why is heat energy produced as a by-product of energy transformation considered “unusable energy?”
A. Because the heat energy can’t be used again
B. Because using that heat produces momentum
C. Because heat causes entropy.
D. Because energy can’t be created/destroyed.
E. None of the above

**It is said that heat can still be used although transforming it to another form of energy will again produce heat, which is impractical.  I can't find the best answer among these but I think it's not None of the above.

5. Fluid buoyancy is caused by:
A. Fluid pressure being density dependent.
B. Fluid pressure being very strong.
C. Differences in air temperature
D. Differences in fluid speed.
E. None of the above.

6. Predict what will happen if two balls traveling in opposite directions with the same speed and mass collide with each other if
the collision is a perfectly elastic collision.  
A. After collision, the velocity of one ball will be higher than the other
B. After collision, the velocity of both balls will still be the same
C. After collision, their velocity will be interchanged
D. After collision, their velocity will be zero
E. None of the above


I would appreciate short explanations. Thanks guys!

1) momentum is the state that an object wants to preserve it's condition, if it is standing still or if it is moving with a steady speed, it wants to stay the same, but if you change it's speed you are changing it's momentum; changing speed means causing acceleration.
2) D
3) Here it stopped because it was loosing it's energy due to the friction, friction with air and also friction in the joints. I think choice (C) is correct.
4) I am sure that B, C and D are wrong!
5) (E), Pressure depends on depth in fluids, and when an object is floating in the fluid it has different pressures on the top and it's bottom, this causes the buoyancy force.
6) as far as it is perfectly elastic they hit each other and move back with the same velocities, they won't loose energy. (C)