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Chapter 6: Q57P (page 144)
A puck of mass slides in a circle of radiuson a frictionless table while attached to a hanging cylinder of massby means of a cord that extends through a hole in the table (Fig. 6-43). What speed keeps the cylinder at rest?
The speed that keeps the cylinder at rest is .
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A student wants to determine the coefficients of static friction and kinetic friction between a box and a plank. She places the box on the plank and gradually raises one end of the plank. When the angle of inclination with the horizontal reaches, the box starts to slip, and it then slides 2.5 mdown the plank in 4.0 sat constant acceleration. What are
(a) the coefficient of static friction and
(b) the coefficient of kinetic friction between the box and the plank?
In Fig. 6-57, a stuntman drives a car (without negative lift) over the top of a hill, the cross section of which can be approximated by a circle of radius R = 250 m. What is the greatest speed at which he can drive without the car leaving the road at the top of the hill?
Block B in Fig. 6-31 weighs .The coefficient of static friction between block and table is ; angle is ; assume that the cord between B and the knot is horizontal. Find the maximum weight of block A for which the system will be stationary?
Engineering a highway curve.If a car goes through a curve too fast, the car tends to slide out of the curve. For a banked curve with friction, a frictional force acts on a fast car to oppose the tendency to slide out of the curve; the force is directed down the bank (in the direction water would drain). Consider a circular curve of radius R 200 mand bank angle u, where the coefficient of static friction between tires and pavement is. A car (without negative lift) is driven around the curve as shown in Fig. 6-11. (a) Find an expression for the car speed that puts the car on the verge of sliding out.
(b) On the same graph, plot versus angle u for the range , first for(dry pavement) and then for(wet or icy pavement). In kilometers per hour, evaluatefor a bank angle ofand for
(c)and
(d). (Now you can see why accidents occur in highway curves when icy conditions are not obvious to drivers, who tend to drive at normal speeds.)
Continuation of Problem 8. Now assume that Eq. 6-14 gives the magnitude of the air drag force on the typical stone, which presents to the wind a vertical cross-sectional area ofand has a drag coefficient C of. (a) In kilometers per hour, what wind speedalong the ground is needed to maintain the stone’s motion once it has started moving? Because winds along the ground are retarded by the ground, the wind speeds reported for storms are often measured at a height of. Assume wind speeds are times those along the ground. (b) For your answer to (a), what wind speed would be reported for the storm? (c) Is that value reasonable for a high-speed wind in a storm?
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