Work and Kinetic Energy of weight

AI Thread Summary
A 20.0-N weight slides down a rough inclined plane at a 30.0-degree angle, starting from rest and reaching a speed of 15.0 m/s after 150 m. The initial calculation of work done against friction was incorrectly estimated at around 2600 J. The discussion emphasizes the importance of identifying the correct forces at play, specifically distinguishing between conservative forces like gravity and non-conservative forces like friction. Participants suggest using conservation of energy principles to accurately determine the work done against friction. Ultimately, understanding the relationship between work and the forces involved is crucial for solving the problem correctly.
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Homework Statement



A 20.0-N weight slides down a rough inclined plane which makes an angle of 30.0o with the horizontal. The weight starts from rest and gains a speed of 15.0 m/s after sliding 150 m. How much work is done against friction? Use g = 10 m/s2.

Homework Equations



W = Fd cos θ

The Attempt at a Solution



I substituted it in the equation and got around 2600 J but the answer is wrong.

Can anyone help me out?

Thanks a lot before hand
 
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Try using conservation of energy.
150m is the hypotenuse, what is the length of the opposite side of the triangle formed?
 
rock_star said:

Homework Equations



W = Fd cos θ

The Attempt at a Solution



I substituted it in the equation and got around 2600 J but the answer is wrong.


That's because (for one) you used the wrong force.
a). What force is burning up your mechanical energy: gravity or friction?
b). Stated another way, Which force is non-conservative: gravity or friction?


(Here's a hint: "Work done against friction" = minus "the work done BY friction")
 

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