Newton's Second Law Homework: Forces, Accelerations, Angles

[Angelnomahou]

Homework Statement

The two forces F⃗ 1 and F⃗ 2 shown in (Figure 1) act on a 29.0-kg object on a frictionless tabletop. Suppose that F1 = 10.8 N , and F2 = 19 N .

A. Determine the magnitude of the net force on the object for the diagram (a) in the figure.

B.Determine the angle between the positive x-axis and the net force F⃗ Ra on the object for the diagram (a), measured countercockwise.

C. Determine the magnitude of the acceleration of the object for the diagram (a).

D. Determine the magnitude of the net force on the object for the diagram (b) in the figure.

E. Determine the angle between the positive x-axis and the net force F⃗ Rb on the object for the diagram (b), measured countercockwise.

F. Determine the magnitude of the acceleration of the object for the diagram (b)

I've tried to solve it these way:
a=10.8+19/29
a=0.37+0.66
a=√0.37²+0.66²
a=0.76
And that gives me aceleration, but I've tried to solve the aceleration for the object in diagram 2 the same way and the computer says it's wrong.
I really don't have idea of how analize the rest of the problem.

 

[gneill]

Hello Angelnomahou.

You must show your own attempt at a solution (what you've tried) before any help can be offered. Helpers need to see what you've tried so that they can determine what help you require. Helpers will not do your homework for you.

 

[Angelnomahou]

I don't know what I have done, I just want to understand, please, it dosent metter if no one gives me the answer, I want to learn how to solve this kind of things, I know helpers don't have to do my homework for me, can some one explain me with another similar problem?
Please, the answer doesn't matter.

 

[jedishrfu]

Try googling on forces in two dimensions. You will find quite few resources. One such source is Khan Academy on Physics with a track on forces in two dimensions. You could start at the beginning and catch up and as you learn more in class back it up by reviewing it on Khans Academy.

Here's another resource with problems to solve and audio commentary to walk you through the solution.

http://www.physicsclassroom.com/calcpad/vecforce/problems

In your problem, you need to understand that forces add like vectors. Your proposed solutions add the forces like scalar values and that won't work as you've discovered. In the part a problem, imagine you are standing at the origin with a rope around you one end is held by your friend standing to the west at say x=-10 and another friend holding the other end of the rope is standing to the south at x=0 y=-10 and both pull you toward them. What will happen?

Well, if they pull too hard, they won't be your friends much longer. If they pull with the same strength of say 10 Newtons then you will move southwest. If the friend to the west pulls you more strongly then you will move west southwest. Do you see how that works?

Now you must use vector math to do the problem and get a more exact answer.

 

[Angelnomahou]

Thanks, for the link and the other pages, ther are really usefull, I will practice there now on.
You really helped me, and there are no words to express how gratefull I feel. Thank you.

 

[God Jr]

Well, if they pull too hard, they won't be your friends much longer.

Epic