At the end of the semester, you are loading your geat into a van togo home. In l

Question

At the end of the semester, you are loading your geat into a van togo home. In loading the van, you can either lift a 45.0kgcrate straight up (method 1) or push it up a 3.00m long ramp thatis inclined at an angle above the horizontal (method2). In both methods, the crate is moved at a constant speed,and the vertical distance from the ground to the floor of the vanhas the same value h. In method 1, no friction is present. Inmethod 2, however, a frictional force does -485J of work onthe crate. In applying your nonconservative pushing force tothe crate, you do twice as much work in method 2 as in method1. Find the angle .
answer: 21.5o
PS: I don't know why i'm getting -21.5o and i use -465=mg(3sin) to solve for . do you know how to eliminatethe negative sign in front of 21.5o?

Explanation / Answer

By setting the -465 equal to mgh, you're essentially saying thatthe friction force is decreasing your height by(3*sin()). So the equation is telling you the angle ofthe ramp that would decrease your height by that amount. It should be 465 = mgh. This means that the work required to liftthe box a height h is 465. Because this implies lifting, the thetawill be positive. Hope that helps.

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