Physics + tension

[br2pi5]

Having some trouble understanding these questions. I'd appreciate the help!

1) the 3kg of clothes one, what would be the set up?
2) the other question, I set it up as sin45 = Ft/T1, so Ft= T1sin45 which then equals 300N (Fg). Is that right?

 

[br2pi5]

Also, shouldn't this be Fg=mgcos(angle) because it's on an incline?

 

[DelayedGratification]

This question is simply asking you for force due to gravity, nothing else. Slightly tricky

 

[BerkReviewTeach]

Also, shouldn't this be Fg=mgcos(angle) because it's on an incline?

If they were asking for the magnitude of the normal force, then you are correct. But they have asked for the gravitational force and given you extraneous information.

 

[BerkReviewTeach]

Having some trouble understanding these questions. I'd appreciate the help!

1) the 3kg of clothes one, what would be the set up?
2) the other question, I set it up as sin45 = Ft/T1, so Ft= T1sin45 which then equals 300N (Fg). Is that right?

For the kid on a pendulum question, you have set it up correctly, where T = mgcos(theta) at the apex, where v = 0, so mv2/r = 0.

For the clothesline question, you need to draw a picture. Initially you have a horizontal cable that is 6 ft long. It then sags in the middle to a point that is lowered by 3 ft. So you have a scenario where the tension must be found using a triangle. The triangle has vertical side of 3 ft (the amount it sags). It has a horizontal side of 3 ft (half to the original ft m line). This means it's a 45-45-90 triangle and the hypothenuse represents the tension. However, there are TWO cables holding the mass up, so you need to consider BOTH. Each side is responsible for supporting 15 N vertically. So if you look back at your triangle, the vertical side is 15 N. Because it is a 45-45-90 triangle, the hypotenuse is 15(root 2) N. The total tension, for both lines, is 2 x 15(root2) N = 30(root2) N.