Physics final exam review - please help!

Well see, this is why I'm here then!

Here are my answers:

2. The apparent weight is lighter than the actual weight because of newtons second law. The true weight and the normal force are acting on the person. So the apparent weight= mg +ma

3.Pulling your arm back will reduce the force because you extend the impulse over a greater period of time, which reduces the impact of the force.

4. I'm not too sure on this one, but I think the ball will come out at a 90 degree angle because it is still influenced by the rotational momentum, but doesn't have the string tension there to keep it on course anymore, so it goes off in a new direction?

Quote by Newton A body persists its state of rest or of uniform motion unless acted upon by an external unbalanced force.

That is one phrasing for Newton's first law of motion. Uniform motion is motion in a straight line at a constant velocity. Though once the string breaks, you still have gravity to consider.

There's no "momentum of the rotation" acting on the ball as soon as the string can provide no tension. That's just an illusion. Perform a simple experiment if you'd like. Twirl a keychain around your finger, and have it slip off at some point, it won't be moving in loops, but it'll just go off in a straight line (Well, projectile motion due to gravity, to be precise)

5. A. potential energy is added to the pendulum prior to release, the pendulum wants to get back to equilibrium and it will take energy to do so.
B. kinetic energy is the greatest just as it swings through the equilibrium point on its way down, because it is assisted by gravity?
C. The potential energy is highest when the pendulum is at the top of each swing, I don't know how to explain why though.

6. The frictional force is necessary to negotiate a curve, and gravitational forces are not acting in the right direction to be able to help the car through the curve.

Again, I'll mention that any curve can be approximated by a circular arc at some limit (Or at least so I've been told, sorry I can't cite a good proof of this)
For circular motion, what is the net force in the radial direction?
Look at a free-body diagram of the car, I suggest you draw it from a cross section of the elevated curve, and look at all the forces you've got acting on it. Remember that it is undergoing circular motion (Which is what's helping it get through the curve) and that it is neither slipping up the curve, nor down. If you still need more help, I'll attach a diagram clarifying my point.
A good question to ask right about now is whether you're familiar with fictitious forces?

7. The sled can not climb a hill higher than its starting point because it only started with a certain amount of potential energy, and since some is lost to frictional forces, there will not be enough to climb a taller hill.

I'm fairly certain you are to assume smooth surfaces unless told otherwise.
What is the sled's initial energy? Is it greater than/equal/less than the potential energy at the hump ever so slightly over the height of its initial height?
Remember it didn't just slide off the hill, it was PUSHED.

8. There is an advantage with longer contact time, this increased the impulse and puts a greater force on the bat. The bat speed is what creates the force, which is the other part of the impulse equation. J = FdeltaT. Increasing the bat speed will also increase the impulse, making the ball go further.

Again, you are correct, but your reasoning is bogged down by poor terminology.
[tex]J\equiv \frac{dP}{dt} \Delta t[/tex]
That's our starting point.
When you hit the ball with the bat, you are changing the ball's momentum. You can think of it as transferring the bat's momentum to the ball.
The longer the two remain in contact, the bigger the change in momentum will be for the ball. And that's what you're trying to achieve. (Greater momentum=greater velocity)
The faster you swing the bat, the more initial momentum you're introducing to the system. There's more momentum available to "transfer" to the ball.
Note that your mathematical argument regarding bat speed falls apart, there is no "velocity of the bat" factor in the definition of impulse as you've presented it.

9.The airbag does the same thing as moving your hand back when catching the baseball, extends the impulse over a greater period of time, reducing the impact you feel.

Exactly. The longer you spread the impulse over, the lower the average force.

10. I had to guess at this one, do you swing the bag of oranges back and forth, constantly changing your center of gravity, causing you to move in the direction the oranges are going?

This would be pointless, since you'd just oscillate around your center of gravity, you want progress!
Think about conservation of momentum and about throwing the oranges.

11. this is a transverse wave because the force you are exerting to create these waves is perpendicular to the direction of the waves.

Can't help you there, haven't studied waves yet.

12. It is possible for 2 waves traveling in the same direction to create a smaller wave, as long as the 2 waves are out of phase with eachother, creating interference and thus a smaller wave is produced.

Well, interference is something I'm familiar with. And yes, this is a correct explanation. If the two waves are out phase enough, the resultant wave will be of a lower amplitude, even 0!

13. Increased tension on a guitar string will increase the frequency and decrease the wavelength of the standing waves. I'm sure there is an equation that proves this, but I'm not sure what it is.

Again, can't help you here. :X

14. I'm pretty clueless on this one.

Think Doppler effect, look over your class notes, it should be in there somewhere. It's pretty simple on an intuitive level, too, though.
Without getting into the precise math of it all, this link from NASA should show you what you need to know.
http://www.grc.nasa.gov/WWW/K-12/airplane/doppler.html

15. Object A will be easier to set into rotational motion, but I don't understand the physics behind this.

This is a question of moments of inertia. If you've delved deeply into rotational motion, this should be a concept you're familiar with. If not, consider the following:
For an object undergoing rotational motion under an angular velocity [tex]\omega[/tex], its momentary LINEAR velocity is [tex]\omega r[/tex] where [tex]r[/tex] is the distance to the axis of rotation (Proof of this is available through VERY simple circle geometry)
To change this angular velocity, that is to say, to rotate the object, you would need to change its linear velocity. Changing the linear velocity of an object with mass (Changing its momentum) requires force.
For two objects of the same mass, undergoing the same angular acceleration, but at different distances from the axis of rotation then, you can see that greater force is required for the object that is further away. So it is easier to rotate the object that's close.

16. Gravity is acting on the person but what is the other force? I don't think its friction because the person is at rest. Could it be the floor acting on the person or a normal force or something?

It IS the normal force. The person is being pulled down by gravity, pushed into the floor. And yet, he remains at rest. The force responsible for this is the normal force.
Now be careful of the pitfall this question has in store. The gravitational pull and the normal are not an action-reaction pair.
The reaction force to the earth pulling the man is the man pulling the earth, and the reaction force to the normal force, is a normal force of equal magnitude going in the opposite direction, into the ground. Action-reaction pairs each act on different masses.

17. The velocity the ball is rolling at is not an important factor when calculating the time it takes to hit the floor, because this is only dependent on gravity, and the height that the ball falls from.

Yep, that's correct. Mathematically speaking, once it leaves the edge of the table, its initial velocity in the [tex]y[/tex] direction is 0, so only the force of gravity determines how long it takes for it to fall.

18. You will see the lighting before you hear the thunder because light waves travel faster than sound waves. I don't really know what physics explanation he is looking for other than that?

At this level you can just cite empirical fact, I think. Light waves travel much faster in air than do sound waves.

19. Sound waves cannot travel through a vacuum because the waves need air particles to move in, and without them, there would be no sound waves.

This is correct, but I'd just change "air particles" to "medium." Since sound waves can propagate in many different materials.

20. The bird increases the potential energy of the clam when it takes it from the ground, when the bird drops the clam, gravity is acting to bring the clam back to earth. Then there is a collision between the clam and the rock where they both exert a force on eachother, but energy is always conserved.

You've missed a couple of things.
The bird increases the potential energy of the clam by lifting it above the plane of reference (The ground).
When it is dropped, gravity performs work on it, converting the potential height energy into kinetic energy.
Upon impact, the clam and the rock exert equal forces on each-other. Momentum is conserved in the collision, but a lot of energy is lost to internal disorder (Heat and deformation).
Remember, unless you're told otherwise, a collision is not completely elastic.

I feel like I have an idea what the answers are, I just can't recall the equations or laws that explain them.