(a) When switched on, the trimmer speeds up from 0 to 2 700 rev/min in 0.200 s. What average power is delivered to the head by the trimmer motor while it is accelerating? w (b) When the trimmer is cutting grass, it spins at 1 930 rev/min and the grass exerts an average tangential force of 6.80 N on the outer end of the cord, which is still at a radial distance of 16.0 cm from the outer edge of the spool. What is the power delivered to the head under load? w

(a) When switched on, the trimmer speeds up from 0 to 2 700 rev/min in 0.200 s. What average power is delivered to the head by the trimmer motor while it is accelerating? w (b) When the trimmer is cutting grass, it spins at 1 930 rev/min and the grass exerts an average tangential force of 6.80 N on the outer end of the cord, which is still at a radial distance of 16.0 cm from the outer edge of the spool. What is the power delivered to the head under load? w

Physics for Scientists and Engineers: Foundations and Connections

1st Edition

ISBN:9781133939146

Author:Katz, Debora M.

Publisher:Katz, Debora M.

Chapter12: Rotation I: Kinematics And Dynamics

Section: Chapter Questions

Problem 71PQ: Three forces are exerted on the disk shown in Figure P12.71,and their magnitudes are F3 = 2F2 = 2F1....

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A copper rod with length 1.4 m and cross-sectional area 2.0 cm2 is fastened to a steel rod of length L and cross-sectional area 1.0 cm2. The compound structure is pulled on each side by two forces of equal magnitude 6.00 104 N (Fig. P14.57). Find the length L of the steel rod if the elongations (L) of the two rods are equal. Use the values Ysteel = 2.0 1011 Pa and YCu = 1.1 1011 Pa. FIGURE P14.57
Three forces are exerted on the disk shown in Figure P12.71,and their magnitudes are F3 = 2F2 = 2F1. The disks outer rimhas radius R, and the inner rim has radius R/2. As shown in thefigure, F1 and F3 are tangent to the outer rim of the disk, and F2 is tangent to the inner rim. F3 is parallel to the x axis, F2 is parallel to the y axis, and F1 makes a 45 angle with the negative x axis. Find expressions for the magnitude of each torque exertedaround the center of the disk in terms of R and F1. FIGURE P12.71 Problems 71-75
The lintel of prestressed reinforced concrete in Figure P12.27 is 1.50 m long. The concrete encloses one steel reinforcing rod with cross-sectional area 1.50 cm2. The rod joins two strong end plates. The cross-sectional area of the concrete perpendicular to the rod is 50.0 cm2. Youngs modulus for the concrete is 30.0 109 N/m2. After the concrete cures and the original tension T1 in the rod is released, the concrete is to be under compressive stress 8.00 106 N/m2. (a) By what distance will the rod compress the concrete when the original tension in the rod is released? (b) What is the new tension T2 in the rod? (c) The rod will then be how much longer than its unstressed length? (d) When the concrete was poured, the rod should have been stretched by what extension distance from its unstressed length? (e) Find the required original tension T1 in the rod. Figure P12.27
The pressure increases by 1.0 x 104 N/m2 for every meter of depth beneath the surface of the ocean. At what depth does the volume of a Pyrex (bulk modulus 2.6 x 1010 N/m2) glass cube, 6.8 x 10-2 m on an edge at the ocean's surface, decrease by 7.5 x 10-10 m3?
A solid ball 300 cm in diameter is submerged in a lake of such depth that pressure exerted by water is 9.8x10^4 N/m^2. Find the change in volume of the ball at this depth. Bulk of the modulus of the material of the ball is 10^12 N/m^2. [1.386 c.c.]
2. a solid steel sphere with a radius of 2.0m falls off a ship and sinks to a depth where the pressure is 15mn/m2. the bulk modulus for this steel is 1.6x10^11N m2. what is the change in the radius? (m=mega + 1x10^6) a. -0.021mm b. -0.062 c. -0.19mm d. -0.42mm
A section of uniform pipe is bent into an upright U shape and partially filled with water, which can then oscillate back and forth in simple harmonic motion. The inner radius of the pipe is r = 0.024 m. The radius of curvature of the curved part of the U is R = 0.23 m. When the water is not oscillating, the depth of the water in the straight sections is d = 0.37 m. Enter an expression for the mass of water in the tube, in terms of the defined quantities and the density of water, ρ. Use the approximation r << R. Calculate the mass of the water, in kilograms. Take ρ = 1000 kg/m3. Enter an expression for the force constant of the U-shaped column of water when displaced from equilibrium, in terms of the defined quantities, ρ, and g. This constant is analogous to the spring constant in Hooke’s law. Find the value of the force constant, in newtons per meter. Take ρ = 1000 kg/m3 and g = 9.81 m/s2. Calculate the period of oscillation, in seconds.
A solid steel sphere with a radius of 2.0 m falls off a ship and sinks to a depth where the pressure is 15 MN/m2. The bulk modulus for this steel is 1.6 × 1011 N/m2. What is the change in the radius of the sphere?
A 1000-kg object hangs from the lower end of a steel rod 5.0 m long that is suspended vertically. The diameter of the rod is 0.80 cm and Young's modulus for the rod is 210,000 MN/m2. What is the elongation of the rod due to this object? choices: 0.12 cm 0.46 cm 0.047 cm 1.2 cm 1.8 cm
A solid copper cube has an edge length of 85.5 cm. How much stress must be applied to the cube to reduce the edge length to 85.0 cm? The bulk modulus of copper is 1.4*1011 N/m2.
A wire stretches from 2000 mm to 2005 mm when a 500-N box hangs from one end of it. The wire has a cross sectional area of 0.01 cm2. Calculate the Young's modulus of the wire. a. 5.0 × 1012 N/m2 b. 1.0 × 109 N/m2 c. 2.0 × 1011 N/m2 d. 2.0 × 109 N/m2 e. 1.0 × 1011 N/m2
A 1000-kg object hangs from the lower end of a steel rod 5.0 m long that is suspended vertically. The diameter of the rod is 0.80 cm and Young's modulus for the rod is 210,000 MN/m2. What is the elongation of the rod due to this object? Group of answer choices a. 0.12 cm b. 0.46 cm c. 0.047 cm d. 1.2 cm e. 1.8 cm