Chapter 4: Problem 18
True or false: A physics book on a table will not move at all if and only if the net force is zero.
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Chapter 4: Problem 18
True or false: A physics book on a table will not move at all if and only if the net force is zero.
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A load of bricks of mass \(M=200.0 \mathrm{~kg}\) is attached to a crane by a cable of negligible mass and length \(L=3.00 \mathrm{~m}\). Initially, when the cable hangs vertically downward, the bricks are a horizontal distance \(D=1.50 \mathrm{~m}\) from the wall where the bricks are to be placed. What is the magnitude of the horizontal force that must be applied to the load of bricks (without moving the crane) so that the bricks will rest directly above the wall?
In a physics class, a 2.70 - g ping pong ball was suspended from a massless string. The string makes an angle of \(\theta=15.0^{\circ}\) with the vertical when air is blown horizontally at the ball at a speed of \(20.5 \mathrm{~m} / \mathrm{s}\). Assume that the friction force is proportional to the squared speed of the air stream. a) What is the proportionality constant in this experiment? b) What is the tension in the string?
A \(2.00-\mathrm{kg}\) block is on a plane inclined at \(20.0^{\circ}\) with respect to the horizontal. The coefficient of static friction between the block and the plane is \(0.60 .\) a) How many forces are acting on the block? b) What is the normal force? c) Is this block moving? Explain.
A nanowire is a (nearly) one-dimensional structure with a diameter on the order of a few nanometers. Suppose a \(100.0-\mathrm{nm}\) long nanowire made of pure silicon (density of \(\mathrm{Si}=2.33 \mathrm{~g} / \mathrm{cm}_{3}\) ) has a diameter of \(5.0 \mathrm{nm}\). This nanowire is attached at the top and hanging down vertically due to the force of gravity. a) What is the tension at the top? b) What is the tension in the middle? (Hint: Treat the nanowire as a cylinder of diameter \(5.0 \mathrm{nm}\) leneth 100 made of silican
A suitcase of weight \(M g=450\). N is being pulled by a small strap across a level floor. The coefficient of kinetic friction between the suitcase and the floor is \(\mu_{k}=0.640 .\) a) Find the optimal angle of the strap above the horizontal. (The optimal angle minimizes the force necessary to pull the suitcase at constant speed.) b) Find the minimum tension in the strap needed to pull the suitcase at constant speed.
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