Need help, physics how things work

[BEEFAROO]

Hey all,
Im doing one of my 14 physcis hws, which are comprised of 10 questions, yet im stuck on a couple of em.
Any help would be appreciated, my aims M0n3y0nf1r3, but feel free to post.
This is for non physics majors but im still confused :>?

When a modern car crashes into a tree and comes to an abrupt stop, the driver's face and chest collide with an air bag rather than with the steering wheel. The driver's chances of serious injury are reduced by hitting the air bag rather than the steering wheel because the driver transfers

-less momentum to the air bag than he would to the steering wheel.
-the same amount of momentum to the air bag as he would to the steering wheel, but he does it with larger force due to the air bag.
-more momentum to the air bag than he would to the steering wheel.
-the same amount of momentum to the air bag as he would to the steering wheel, but he does it with smaller force due to the air bag.


After clearing the bar in the high jump, you land softly on a giant mattress. Landing on the mattress is much more comfortable than landing on a sand heap of equal size because

-you transfer less momentum to the mattress in coming to a stop than you would have transferred to the sand heap in coming to a stop.
-the force that the mattress exerts on you to stop your descent is much less than the force that the sand heap would have exerted on you.
-you transfer more momentum to the mattress in coming to a stop than you would have transferred to the sand heap in coming to a stop.
-your velocity is less as you land on the mattress than it would have been if you'd landed on the sand heap.


The moment of inertia of a long thin rod is minimum when it is spinning about an axis

-down the center of the rod lengthwise.
-through the center of the rod, perpendicular to its length.
-through the end of the rod, perpendicular to its length.
-The moment of inertia is a constant, so A, B, and C are all equal.

[recipro]

1. Conservation of momentum. Force = mass * acceleration. Mass is obv constantly, so figure out which has lower force...

2. Conservation of momentum again.

3. MOI. If mass density is constant, I = mr^2. So pick the line that minimizes r^2 (for all points on the rod summed, etc.. The integral of r^2). Should be pretty obvious.

Hope this helps.

[BEEFAROO]

Thanks [img]/images/graemlins/laugh.gif[/img]