Why Am I Struggling with Newton's Laws Problems?

[jordanfeld]

I'm having a lot of trouble trying to figure out some of these problems. If people could help me, it'd be greatly appreciated!

1. A 50.0-kg person takes a nap in a backyard hammock. Both ropes supporting the hammock are at an angle of 15.0° above the horizontal. Find the tension of the ropes.

-I used Fy₂ = Ft₂ sin (°). I got 1895.3 for an answer, yet I don't think this is right at all.


2. Your friend's 12.6-g graduation tassel hangs on a string from his rear-view mirror.
(a) When he accelerates from a stoplight, the tassel deflects backward toward the rear of the car. Explain.
(b) If the tassel hangs at an angle of 6.2° relative to the vertical, what is the acceleration of the car?
(c) Find the tension in the string holding the tassel.
(d) At what angle to the vertical will the tension in the string be twice the weight of the tassel?

-I found that the tassel is .0126-kg.
-For (a) I said "the sudden stop in acceleration causes it to go back, because there is nothing to stop it's movement."
-For (b) I wrote the equation F_net = F_g - F_n


Thanks for any help, I am just very lost. If you can even reccomend any detailed websites, that'd be great as well. :)

 

[ideasrule]

I'm having a lot of trouble trying to figure out some of these problems. If people could help me, it'd be greatly appreciated!

1. A 50.0-kg person takes a nap in a backyard hammock. Both ropes supporting the hammock are at an angle of 15.0° above the horizontal. Find the tension of the ropes.

-I used Fy₂ = Ft₂ sin (°). I got 1895.3 for an answer, yet I don't think this is right at all.

You're very close, but you forgot that the person's weight is supported by two ropes, not one. If you divide 1895 by 2, you'd get the right answer.

2. Your friend's 12.6-g graduation tassel hangs on a string from his rear-view mirror.
(a) When he accelerates from a stoplight, the tassel deflects backward toward the rear of the car. Explain.
(b) If the tassel hangs at an angle of 6.2° relative to the vertical, what is the acceleration of the car?
(c) Find the tension in the string holding the tassel.
(d) At what angle to the vertical will the tension in the string be twice the weight of the tassel?

-I found that the tassel is .0126-kg.
-For (a) I said "the sudden stop in acceleration causes it to go back, because there is nothing to stop it's movement."
-For (b) I wrote the equation F_net = F_g - F_n

For a: What is a "sudden stop in acceleration"? The car's just accelerating; there's no stop in its acceleration. Otherwise, your explanation is correct: the thing has inertia and doesn't want to change its speed.

For b, what's Fn? Try drawing a free-body diagram of the tassel, labeling the external forces, and writing out Newton's second law for both the x and y directions. After that, you just have to solve the equations.

 

[kerimek]

Dear student,

I understand that you are having trouble with these Newton's Laws problems. I would suggest reviewing the basic principles of Newton's Laws and applying them to each problem step by step. It's important to identify all the forces acting on the objects in question and use the appropriate equations to solve for the unknown variables.

For the first problem, you correctly used the equation Fy2 = Ft2 sin(°) to find the tension in the ropes. However, it's important to note that the angle given is measured above the horizontal, not below. So the correct equation should be Fy2 = Ft2 sin(15°). Also, make sure to convert the person's mass from kg to N (Newton) by using the conversion factor 9.8 m/s^2. This should give you the correct answer.

For the second problem, here are some hints to help you solve it:
(a) Think about the direction of the net force acting on the tassel when the car accelerates.
(b) Use the equation Fnet = ma to find the acceleration of the car.
(c) Use the equation Fnet = Fg - Fn to find the tension in the string.
(d) Set the tension in the string equal to twice the weight of the tassel and solve for the angle.

I would also recommend checking out Khan Academy or Physics Classroom for more detailed explanations and practice problems on Newton's Laws. Keep practicing and don't hesitate to ask for help when needed. Good luck!