I'm finishing up my WebAssign homework for tomorrow and I'm having a few problems with some of the questions and I'm hoping jsp can help me out

I'm terrible in Physics btw and I'm extremely glad this is the last science class I have to take lol. Just point me in the right direction on how to solve these questions please. There's really no point if you do them for me and just give me an answer...I'd still have no idea how to do them


A boat moves through the water with two forces acting on it. One is a 1700 N forward push by the water on the propeller, and the other is an 1000 N resistive force due to the water around the bow.
(a.) What is the acceleration of the 1300 kg boat?

-I already got his answer of .54 m/s^2 correct

(b.) If it starts from rest, how far will it move in 8.0 s?

-I got 17.28 m correct as well

(c.) What will its velocity be at the end of that time?

- Have no idea on how to calculate this. I got it wrong a few times and gave up



A 4.5 g bullet leaves the muzzle of a rifle with a speed of 318 m/s. What force (assumed constant) is exerted on the bullet while it is traveling down the 0.83 m long barrel of the rifle?

-I have absolutely no idea how to do this one at all lol


The force exerted by the wind on the sails of a sailboat is 360 N north. The water exerts a force of 240 N east. If the boat (including its crew) has a mass of 290 kg, what are the magnitude and direction of its acceleration?

- Another one that has me completely lost



Somebody plz!
Thanks

This post was edited by Jangoon244 on Feb 17 2009 06:18pm

I havent actually done this but here are some hints to help you out.

1c. Since you know that your boat is at rest, know acceleration, know time, know distance, you can pick any of the kinematics eqns and you should get the right answer.

Bullet question
I believe this one is a conceptual question, but its kind of ambiguous. If the question is asking what the force exerted on the bullet AFTER it is propelled but still in the barrel, then the answer would be the force of friction or nothing. However if it is asking you what the initial force is that propels the bullet, that is a little harder, and I will probably have to think about that a little more and get back to you.


Boat question.
Make a triangle of the forces. The one pointing north and the one pointing east. The values of the triangle legs will be the magnitude of the force. The hypotenuse of this triangle will be the net force experienced. This is just a vector addition problem, look at how to add vectors in your textbook if I am unclear. Then, after you get this, all you have to do is use the F=ma equation. Acceleration is the only vector quantity that gives force its vector quantity. So its direction should be the same as your net force.


Well I hope that helps, pm me if you have any questions.

For the bullet one, find the acceleration as it goes through the barrel, easy to do this as you know initial velocity is 0ms^-1, the final velocity is 318ms^-1 and the barrel length is 0.83m
Then times the acceleration by 4.5x10^-3 as you want the mass in kg

For the boat question, use pythagoras to find the magnitude of the force, then f=ma to find acceleration. Then construct a triangle and use trigonometry to find the angle, having 360N as the adjacent side 240N as opposite and the resultant force you calculated as the hypotenuese. This way the angle is from north, so you can give it as a bearing.