We are given the following equations: Energy - Potential Energy --> PE = mgh - K

Question

We are given the following equations:

Energy

- Potential Energy --> PE = mgh

- Kinetic Energy --> KE = 1/2mv^2

Work

- Work caused by applied force --> WF = Fd

- Work caused by friction force --> Wf = F(subf)d

- Work caused by gravity --> Wg = mg(z2 - z1)

- Work caused by acceleration --> Wa = 1/2 m (v2^2 - v1^2)

Questions:

1) You are pulling a crate across a horizontal floor with a rope for 20m. The rope has 200N of force, at a 45 degree angle off the horizontal. The friction between the crate and the floor is 50N. What is the total net work?

2) A 1200kg automobile accelerates up a hill, increasing its speed from 0m/s to 50m/s along a straight 500 meter stretch of road. If the hill makes an angle of 20 degrees with respect to the horizontal. There is a friction force between the tires and the road of 200N. Find the total net work done by the automobile.

Thank You!

Explanation / Answer

2) Wg= (1200*sin(20))*9.81*500 = 2011078.44 J

Wa = 0.5*1200*(50^2-0^2) = 1500000 J

Wf = 200*500 = 100000 J

Total work = Wg + Wa - Wf = 3411078.443 or 3.41x10^6 J (This is the answer my engineering teacher gave in the answer key)

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