The mysterious sliding stones. Along the remote Racetrack Playa in Death Valley, California, stones sometimes gouge out prominent trails in the desert floor, as if the stones had been migrating. For years curiosity mounted about why the stones moved. One explanation was that strong winds during occasional rainstorms would drag the rough stones over ground softened by rain. When the desert dried out, the trails behind the stones were hard-baked in place. According to measurements, the coefficient of kinetic friction between the stones and the wet playa ground is about 0.80.What horizontal force must act on a 20 kg stone (a typical mass) to maintain the stone’s motion once a gust has started it moving?

A ski that is placed on snow will stick to the snow. However, when the ski is moved along the snow, the rubbing warms and partially melts the snow, reducing the coefficient of friction and promoting sliding. Waxing the ski makes it water repellent and reduces friction with the resulting layer of water. A magazine reports that a new type of plastic ski is especially water repellent and that, on a gentle 230 m slope in the Alps, a skier reduced his top-to-bottom time from 69 s with standard skis to 42 s with the new skis. Old skis acceleration = 0.097 m/s2 New skis acceleration = 0.26 m/s2 Assuming a 3.0° slope, compute the coefficient of kinetic friction for each case. Old skis _______ New skis  _______

The objective of curling, an Olympic discipline, is to throw stones at houses. The stone is a 18 kg block of granite that slides on the carefully prepared ice with a very low coefficient of kinetic friction, μk = 0.0178. With a curling broom the players can increase the friction to get as close as possible to the house, the target pattern embedded in the ice. Frequently an oncoming stone will bump a stone from a previous throw by the competing team. A stone reaches the house with a velocity of 1.2 m/s after traveling the 38 m length of the curling sheet. How fast the stone was going when it was released? The stone did not hit any other stones.

Time left 0:20:32 An amusement park in Dubai has a ramp which is frictionless. A child drops a smooth object and it slides down the ramp and comes down through a height 4 m. What distance is necessary to stop the object on the flat track if the coefficient of friction is 0.4? h. Answer:

You are driving through the Ouachita Mountains at 12m/s. You see a maple-leaf oak (Quercus acerifolia) crossing the road and hit the brakes, 20m away. The coefficient of kinetic friction between your tires and the road is μ_k = 0.7. Will you strike this endangered broadleaf? Justify your answer with a calculation.Your final answer should be the distance you will travel before coming to a stop.

a rock climber on a rock slab. The coefficient of kinetic friction between the climber's rock climbing shoes and the rock is 0.70.  If the climber slide down the rock starting from rest, the amount of time it will take the climber to slide to the edge of the rock slab is?  distance=16.4 m and theta is 68 degrees.

Dandelion seeds have a plume made of thin filaments that create a very large drag coefficient due to subtle aerodynamics as the air moves through and past the plume. The slower terminal speed and longer time in the air provide greater dispersal than would be possible for simple spherical seeds. A 0.63 mg seed has a plume with a cross-section area of 13 mm, and it falls with a terminal speed of 40 cm/s.

You have landed a job in Disney’s Imagineering Department. (Congratulations!) There, you are part of a team that is building a new roller coaster. Several of your coworkers have submitted proposals. Now you have to sit down to select one design that will be prototyped and studied further. Today you are studying the first section of one of those designs. The car is to begin virtually at rest atop a hill. (The cars are just barely pulled over this initial hill.) From there, the car descends until it enters a vertical loop. Rather than a circular loop, this design has a teardrop, or clothoid, design. This shape can be thought of as a large radius circular arc at the bottom and a small radius arc at the top. (That is, the top and bottom can be thought of as portions with two different circular paths.) In this design, the bottom radius of curvature is 40m and the top is 20m. The top of the loop is 60m above the ground. There are a few safety considerations for the roller coaster: The…

An ice hockey puck is sliding over a frictionless horizontal surface with a constant velocity of vo = 10.2 m/s. Find the velocity of the puck after it passes a rough area of length L 6 m and with the kinetic friction coefficient u = 0.33 as shown below. Hint: the mass of the puck is not needed, you can either calculate everything per unit of mass or, if it helps, take m 160 grams. %3D %3D %3D %3D m Vo L The steps to follow: (1) find the initial KE of the puck; (2) find the work done by the friction force (should be negative); (3) find the final kinetic energy as KE; = KE; + W, meaning that some of the initial kinetic energy is lost due to the work done by friction; (4) from the final KE find the final speed. The final speed of the puck, Vf =7.28 X Units m/s %3D If the initial speed of the puck is not high enough the puck will get stuck in the rough area. At what minimal initial speed should the puck move to barely make it through the rough area? The minimal initial velocity, Vmin =…

At Ted's request, Bill pushes the pizza box across the granite countertop towards Ted. When the box leaves Bill's hand it is sliding at 2.60 m/s. The box comes to rest over a distance of 110 cm. What is the coefficient of kinetic friction, uk, between the pizza box and the countertop? (Ignore air drag.)