[lemmonkat]

I'm totally and completely lost on most of these questions.
It's a lot, but it would be a huge help even if anyone could answer even one of them.
Hopefully there isn't a rule to posting multiple questions?

Thank you so much!

3) Net torque produces ____

9) A machine gun fires 55g bullets at the rate of 3 bullets per second. The bullets leave the gun at a speed of 1050 m/s. What is the average recoil force experienced by the machine gun?

10) A .50-kg bomb is sliding along an icy pond with a velocity of 1.75 m/s to the west. The bomb explodes into two pieces. After the explosion, a 0.18 kg piece moves south at 3.5 m/s. What are the components of the velocity of the 0.32-kg piece?

12) A 65.0 kg astronaut is floating toward the front of her stationary ship at 0.30 m/s, relative to the ship. She wishes to stop moving, relative to the ship. She decides to throw away a 3.00 kg book she's carrying. What should the speed and direction of the book be to achieve her goal?

13) A 4.0 kg ball and a 1.5 kg ball are placed at opposite ends of a beam so that the system is in equilibrium. What is the ratio of the lengths to the center of gravity?

14) Define momentum with units.

15) A 0.050 kg tennis ball moving to the right with a speed of 20 m/s is stuck by a tennis racket, causing it to move the left with a speed of 20 m/s. If the ball remains in contact with the racquet for 0.030 s, what is the magnitude of the average force experienced by the ball?

17) A 3.5 kg ball and a 4.5 kg ball have an elastic collision. Before the collision, the 3.5 kg ball was a t rest and the other ball had a speed of 3.5 m/s. What is the kinetic energy of the 3.5 kg ball after the collision? (Hint: find the velocity using the conservation of momentum theorem, then use the equation for KE)

18) A 75 kg man that stands 3 m from the center of gravity on a teeter-totter balances a boy that is 1 m from the center of gravity on the other side of the fulcrum. A) What is the magnitude of the downward force exerted on the fulcrum? B) What is the approximate mass of the boy?

19) One end of a rope is tied to the handle of a horizontally-oriented and uniform door. A force F is applied to the other end of the rope as shown in the drawing. The door has a weight of 150 N and is hinged on the right. What is the magnitude of F at which the door will remain at rest?

23) A uniform 15 kg trap door that is 0.85 m long is oriented horizontally and hinged at the end. What is the magnitude of the torque on the door at the instant that the release is activated and the door can freely rotate?

25) While a car is stopped at a traffic light in a storm, raindrops strike the roof of the car. The area of the roof is 6.5 square meters. Each raindrop has a mass of 4.5 x 10^-4 kg and speed of 1.5 m/s before impact and is at rest after the impact. If, on average at a given time, 200 raindrops strike each square meter, what is the impulse of the rain striking the car?

Thanks again!
-Katie

[Capuchin]

Nobody should answer these for you, it's your work, but I'll give you as many pointers as I can.

torque is a force about a point, and produces rotation.

For the rest, you need to use conservation of momentum, and formulae for impulse.

For momentum mv before = mv afterwards, taking the whole system into account.
As for impulse, it can either be calculated as a force over a length of time (f(delta(t))) or as a change in momentum (mv1-mv2) of an object or system.

I hope these help, I think it should be enough to answer all the questions here.

[Capuchin]

The following was from a private message: Just want to put it here for anyone else with a similar problem :)

Thanks so much for your help :]

I still have a question on 17, though. Most of the problems I don't understand are like this: I can get halfway through and then get stuck.

For 17, I took the conservation of momentum theorem and got this:

(3.5)(0) + (4.3)(3.5)= (3.5)(xf) + (4.3)(xf)
5.05= (3.5)(xf) + (4.3)(xf)

From there, how would you solve for two different velocties if you only have one x value?

I'm not sure if that makes any sense at all.

Ahhh okay.

For an elastic collision, kinetic energy is also conserved!
So you can make another equation using KE, and you will get 2 equations with 2 variables for velocity. You can then solve that simultaneously :)

To say it in a way that is easy to remember:
No energy is lost in an elastic collision