The figure shows the cross section of a road cut into the side of a mountain. What is the least vertical pull fpv that will allow the first worker’s 114 N push to move the crate? (e) If, instead, the second worker pulls horizontally to help out, what is the least pull fpg that will get the crate moving?Ĥ. (a) What is the value offs,max under the circumstances? (b) Does the crate move? (“yes” or “no”) (c) What is the frictional force fr on the crate from the floor? (d) Suppose, next, that a second worker pulls directly upward on the crate to help out. The coefficient of static friction between the crate and the floor is 0.390. A worker pushes horizontally on a 38.0 kg crate with a force of magnitude 114 N. What horizontal force is needed on a stone of typical mass 14 kg to maintain the stone’s motion once a gust has started it moving?ģ. According to measurements, the coefficient of kinetic friction between the stones and the wet playa ground is about 0.751. When the desert dried out, the trails behind the stones were hard-baked in place.

One explanation was that strong winds during the occasional rainstorms would drag the rough stones over ground softened by rain. For years curiosity mounted about why the stones moved. Along the remote Racetrack Playa in Death Valley, California, stones sometimes gouge out prominent trails in the desert floor, as if they had been migrating (see the figure). What is the coefficient of kinetic friction between the pig and the slide? In the figure, a slide-loving pig slides down a certain 38° slide in twice the time it would take to slide down a frictionless 38° slide.

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