Physics of Everyday Phenomena
9th Edition
ISBN: 9781259894008
Author: W. Thomas Griffith, Juliet Brosing Professor
Publisher: McGraw-Hill Education
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Chapter 6, Problem 11CQ
A boy pushes his friend across a skating rink. Because the frictional forces are very small, the force exerted by the boy on his friend’s back is the only significant force acting on the friend in the horizontal direction. Is the change in kinetic energy of the friend greater than, equal to, or less than the work done by the force exerted by the boy? Explain.
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Physics of Everyday Phenomena
Ch. 6 - Equal forces are used to move blocks A and B...Ch. 6 - A man pushes very hard for several seconds upon a...Ch. 6 - Prob. 3CQCh. 6 - In the situation pictured in question 3, if there...Ch. 6 - In the situation pictured in question 3, does the...Ch. 6 - A ball is being twirled in a circle at the end of...Ch. 6 - A man slides across a wooden floor. What forces...Ch. 6 - A woman uses a pulley arrangement to lift a heavy...Ch. 6 - A lever is used to lift a rock, as shown in the...Ch. 6 - A crate on rollers is pushed up an inclined plane...
Ch. 6 - A boy pushes his friend across a skating rink....Ch. 6 - A child pulls a block across the floor with force...Ch. 6 - If there is just one force acting on an object,...Ch. 6 - Prob. 14CQCh. 6 - A box is moved from the floor up to a tabletop but...Ch. 6 - Prob. 16CQCh. 6 - Is it possible for a system to have energy if...Ch. 6 - Prob. 18CQCh. 6 - Which has the greater potential energy: a ball...Ch. 6 - Prob. 20CQCh. 6 - Suppose the physics instructor pictured in figure...Ch. 6 - A pendulum is pulled back from its equilibrium...Ch. 6 - For the pendulum in question 22when the pendulum...Ch. 6 - Is the total mechanical energy conserved in the...Ch. 6 - Prob. 25CQCh. 6 - Prob. 26CQCh. 6 - Prob. 27CQCh. 6 - Prob. 28CQCh. 6 - Prob. 29CQCh. 6 - If one pole-vaulter can run faster than another,...Ch. 6 - Prob. 31CQCh. 6 - Suppose that the mass in question 31 is halfway...Ch. 6 - A spring gun is loaded with a rubber dart. The gun...Ch. 6 - Prob. 34CQCh. 6 - A sled is given a push at the top of a hill. Is it...Ch. 6 - Prob. 36CQCh. 6 - Prob. 37CQCh. 6 - A horizontally directed force of 40 N is used to...Ch. 6 - A woman does 210 J of work to move a table 1.4 m...Ch. 6 - A force of 80 N used to push a chair across a room...Ch. 6 - Prob. 4ECh. 6 - Prob. 5ECh. 6 - Prob. 6ECh. 6 - Prob. 7ECh. 6 - Prob. 8ECh. 6 - A leaf spring in an off-road truck with a spring...Ch. 6 - To stretch a spring a distance of 0.30 m from the...Ch. 6 - Prob. 11ECh. 6 - Prob. 12ECh. 6 - A 0.40-kg mass attached to a spring is pulled back...Ch. 6 - Prob. 14ECh. 6 - A roller-coaster car has a potential energy of...Ch. 6 - A roller-coaster car with a mass of 900 kg starts...Ch. 6 - A 300-g mass lying on a frictionless table is...Ch. 6 - The time required for one complete cycle of a mass...Ch. 6 - The frequency of oscillation of a pendulum is 16...Ch. 6 - Prob. 1SPCh. 6 - As described in example box 6.2, a 120-kg crate is...Ch. 6 - Prob. 3SPCh. 6 - Suppose that a 300-g mass (0.30 kg) is oscillating...Ch. 6 - A sled and rider with a total mass of 50 kg are...Ch. 6 - Suppose you wish to compare the work done by...
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- A particle moves in the xy plane (Fig. P9.30) from the origin to a point having coordinates x = 7.00 m and y = 4.00 m under the influence of a force given by F=3y2+x. a. What is the work done on the particle by the force F if it moves along path 1 (shown in red)? b. What is the work done on the particle by the force F if it moves along path 2 (shown in blue)? c. What is the work done on the particle by the force F if it moves along path 3 (shown in green)? d. Is the force F conservative or nonconservative? Explain. FIGURE P9.30 In each case, the work is found using the integral of Fdr along the path (Equation 9.21). W=rtrfFdr=rtrf(Fxdx+Fydy+Fzdz) (a) The work done along path 1, we first need to integrate along dr=dxi from (0,0) to (7,0) and then along dr=dyj from (7,0) to (7,4): W1=x=0;y=0x=7;y=0(3y2i+xj)(dxi)+x=7;y=0x=7;y=4(3y2i+xj)(dyj) Performing the dot products, we get W1=x=0;y=0x=7;y=03y2dx+x=7;y=0x=7;y=4xdy Along the first part of this path, y = 0 therefore the first integral equals zero. For the second integral, x is constant and can be pulled out of the integral, and we can evaluate dy. W1=0+x=7;y=0x=7;y=4xdy=xy|x=7;y=0x=7;y=4=28J (b) The work done along path 2 is along dr=dyj from (0,0) to (0,4) and then along dr=dxi from (0,4) to (7,4): W2=x=0;y=0x=0;y=4(3y2i+xj)(dyj)+x=0;y=4x=7;y=4(3y2i+xj)(dyi) Performing the dot product, we get: W2=x=0;y=0x=0;y=4xdy+x=0;y=4x=7;y=43y2dx Along the first part of this path, x = 0. Therefore, the first integral equals zero. For the second integral, y is constant and can be pulled out of the integral, and we can evaluate dx. W2=0+3y2x|x=0;y=4x=7;y=4=336J (c) To find the work along the third path, we first write the expression for the work integral. W=rtrfFdr=rtrf(Fxdx+Fydy+Fzdz)W=rtrf(3y2dx+xdy)(1) At first glance, this appears quite simple, but we cant integrate xdy=xy like we might have above because the value of x changes as we vary y (i.e., x is a function of y.) [In parts (a) and (b), on a straight horizontal or vertical line, only x or y changes]. One approach is to parameterize both x and y as a function of another variable, say t, and write each integral in terms of only x or y. Constraining dr to be along the desired line, we can relate dx and dy: tan=dydxdy=tandxanddx=dytan(2) Now, use equation (2) in (1) to express each integral in terms of only one variable. W=x=0;y=0x=7;y=43y2dx+x=0;y=0x=7;y=4xdyW=y=0y=43y2dytan+x=0x=7xtandx We can determine the tangent of the angle, which is constant (the angle is the angle of the line with respect to the horizontal). tan=4.007.00=0.570 Insert the value of the tangent and solve the integrals. W=30.570y33|y=0y=4+0.570x22|x=0x=7W=112+14=126J (d) Since the work done is not path-independent, this is non-conservative force. Figure P9.30ANSarrow_forwardA nonconstant force is exerted on a particle as it moves in the positive direction along the x axis. Figure P9.26 shows a graph of this force Fx versus the particles position x. Find the work done by this force on the particle as the particle moves as follows. a. From xi = 0 to xf = 10.0 m b. From xi = 10.0 to xf = 20.0 m c. From xi = 0 to xf = 20.0 m FIGURE P9.26 Problems 26 and 27.arrow_forwardA particle is subject to a force Fx that varies with position as shown in Figure P7.9. Find the work done by the force on the particle as it moves (a) from x = 0 to x = 5.00 m, (b) from x = 5.00 m to x = 10.0 m, and (c) from x = 10.0 m to x = 15.0 m. (d) What is the total work done by the force over the distance x = 0 to x = 15.0 m?arrow_forward
- Give an example of a situation in which there is a force and a displacement, but the force does no work. Explain why it does no work.arrow_forwardIn Figure 5.5 (a)-(d), a block moves to the right in the positive x-direction through the displacement x while under the influence of a force with the same magnitude F. Which of the following is the correct order of the amount of work done by the force F, from most positive to most negative? (a) d, c, a, b (b) c, a, b, d (c) c, a, d, barrow_forwardA boy starts at rest and slides down a frictionless slide as in Figure P5.64. The bottom of the track is a height h above the ground. The boy then leaves the track horizontally, striking the ground a distance d as shown. Using energy methods, determine the initial height H of the boy in terms of h and d. Figure P5.64arrow_forward
- Suppose the ski patrol lowers a rescue sled and victim, having a total mass of 90.0 kg, down a 60.0° slope at constant speed, as shown in Figure 7.37. The coefficient of friction between the sled and the snow is 0.100. (a) How much work is done by friction as the sled moves 30.0 m along the hill? (b) How much work is done by the rope on the sled in this distance? (c) What is the work done by the gravitational force on the sled? (d) What is the total work done?arrow_forwardA particle moves in one dimension under the action of a conservative force. The potential energy of the system is given by the graph in Figure P8.55. Suppose the particle is given a total energy E, which is shown as a horizontal line on the graph. a. Sketch bar charts of the kinetic and potential energies at points x = 0, x = x1, and x = x2. b. At which location is the particle moving the fastest? c. What can be said about the speed of the particle at x = x3? FIGURE P8.55arrow_forwardA block is placed on top of a vertical spring, and the spring compresses. Figure P8.24 depicts a moment in time when the spring is compressed by an amount h. a. To calculate the change in the gravitational and elastic potential energies, what must be included in the system? b. Find an expression for the change in the systems potential energy in terms of the parameters shown in Figure P8.24. c. If m = 0.865 kg and k = 125 N/m, find the change in the systems potential energy when the blocks displacement is h = 0.0650 m, relative to its initial position. FIGURE P8.24arrow_forward
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