GÖÁL Use conservation of mechanical energy to solve a one-dimensional problem involving gravitational potential energy and spring potential energy. PROBLEM A 50.0 kg circus acrobat drops from a height of 2.00 meters straight down onto a springboard with a force constant of 8.00 x 103 N/m, as in the figure. By what maximum distance does she compress the spring? STRATEGY Nonconservative forces are absent, so conservation of mechanical energy can be applied. At the two points of interest, the acrobat's initial position and the point of maximum spring compression, her velocity is zero, so the kinetic energy terms will be zero. (a) (b) Choose y = 0 as the point of maximum An acrobat drops onto a springboard, causing it to compress. compression, so the final gravitational potential energy is zero. This choice also means that the initial position of the acrobat is y; = h + d, where h is the acrobat's initial height above the platform and d is the spring's maximum compression. SOLUTION Use conservation of mechanical energy. (1) (KE + PEg + PE,); = (KE + PE, + PE,)S The only nonzero terms are the initial 0 + mg(h + d) + 0 = 0 +0 + ½kd? gravitational potential energy and the final spring potential energy. mg(h + d) = ½kd? Substitute the given quantities and rearrange the equation into standard quadratic form. (50.0 kg)(9.80 m/s²)(2.00 m + d) = ½(8.00 × 103 N/m)d² d2 - (0.123 m) d - 0.245 m2 = 0 Solve with the quadratic formula. d = 0.560 m LEARN MORE REMARKS The other solution, d = -0.437 m, can be rejected because d was chosen to be a positive number at the outset. A change in the acrobat's center of mass, say, by crouching as she makes contact with the springboard, also affects the spring's compression, but that effect was neglected. Shock absorbers often involve springs, and this example illustrates how they work. The spring action of a shock absorber turns a dangerous jolt into a smooth deceleration, as excess kinetic energy is converted to spring potential energy. QUESTION Is it possible for the acrobat to rebound to a height greater than her initial height? Explain. (Select all that apply.) O No. The kinetic energy that the acrobat gains on the way down is converted entirely back into potential energy when she reaches the initial height. Yes. Elastic energy is always present in the spring and can give the acrobat greater height than initially. O Yes. The acrobat can provide mechanical energy by pushing herself up while in contact with the springboard. O No. There is no external source of energy to provide the potential energy at a greater height. O Yes. The acrobat can bend her knees while falling and then straighten them as if jumping when bouncing upward again.
GÖÁL Use conservation of mechanical energy to solve a one-dimensional problem involving gravitational potential energy and spring potential energy. PROBLEM A 50.0 kg circus acrobat drops from a height of 2.00 meters straight down onto a springboard with a force constant of 8.00 x 103 N/m, as in the figure. By what maximum distance does she compress the spring? STRATEGY Nonconservative forces are absent, so conservation of mechanical energy can be applied. At the two points of interest, the acrobat's initial position and the point of maximum spring compression, her velocity is zero, so the kinetic energy terms will be zero. (a) (b) Choose y = 0 as the point of maximum An acrobat drops onto a springboard, causing it to compress. compression, so the final gravitational potential energy is zero. This choice also means that the initial position of the acrobat is y; = h + d, where h is the acrobat's initial height above the platform and d is the spring's maximum compression. SOLUTION Use conservation of mechanical energy. (1) (KE + PEg + PE,); = (KE + PE, + PE,)S The only nonzero terms are the initial 0 + mg(h + d) + 0 = 0 +0 + ½kd? gravitational potential energy and the final spring potential energy. mg(h + d) = ½kd? Substitute the given quantities and rearrange the equation into standard quadratic form. (50.0 kg)(9.80 m/s²)(2.00 m + d) = ½(8.00 × 103 N/m)d² d2 - (0.123 m) d - 0.245 m2 = 0 Solve with the quadratic formula. d = 0.560 m LEARN MORE REMARKS The other solution, d = -0.437 m, can be rejected because d was chosen to be a positive number at the outset. A change in the acrobat's center of mass, say, by crouching as she makes contact with the springboard, also affects the spring's compression, but that effect was neglected. Shock absorbers often involve springs, and this example illustrates how they work. The spring action of a shock absorber turns a dangerous jolt into a smooth deceleration, as excess kinetic energy is converted to spring potential energy. QUESTION Is it possible for the acrobat to rebound to a height greater than her initial height? Explain. (Select all that apply.) O No. The kinetic energy that the acrobat gains on the way down is converted entirely back into potential energy when she reaches the initial height. Yes. Elastic energy is always present in the spring and can give the acrobat greater height than initially. O Yes. The acrobat can provide mechanical energy by pushing herself up while in contact with the springboard. O No. There is no external source of energy to provide the potential energy at a greater height. O Yes. The acrobat can bend her knees while falling and then straighten them as if jumping when bouncing upward again.
College Physics
11th Edition
ISBN:9781305952300
Author:Raymond A. Serway, Chris Vuille
Publisher:Raymond A. Serway, Chris Vuille
Chapter1: Units, Trigonometry. And Vectors
Section: Chapter Questions
Problem 1CQ: Estimate the order of magnitude of the length, in meters, of each of the following; (a) a mouse, (b)...
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