4. The mechanical advantage of a pulley system is 10. It takes 130 N of force to lift a crate without the pulley system. a. What is the mass of the crate?
b. How much force needs to applied to the pulley system in order to lift the crate?
c. How much power is exerted by the machine if the crate lifts 750 cm in 2 seconds? Express the units two different ways.

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How much work is done lifting a 9.10 kg box straight up onto a shelf that is 1.80 m high?

Awater slide of length l has a vertical drop of h. abby's mass is m. an average friction force of magnitude f opposes her motion. she starts down the slide at initial speed vi. use work-energy ideas to develop an expression for her speed at the bottom of the slide. then evaluate your result using unit analysis and limiting case analysis. express your answer in terms of the variables h, m, l, vi, f and appropriate constants. vf v f

In a classical model of the hydrogen atom, the electron moves around the proton in a circular orbit of radius 0.053 nm. what is the electron's orbital frequency? what is the effective current of the electron?