Exam #2 Phys 235 WC\'D Name 16. A 0.12 m radius grinding wheel takes 5.5 s to sp

Question

Exam #2 Phys 235 WC'D Name 16. A 0.12 m radius grinding wheel takes 5.5 s to speed up from 2.0 rad/s to 11.0 rad/s. What is the wheel's average angular acceleration? a. 9.6 rad/s2 b. 4.8 rad/s c. 1.6 rad/s d. 0.33 rad/s 17. A planet has 3 times the radius of the Earth, but has the same density as the Earth what is the gravitational acceleration at the surface of the planet? (use g-9.80 m/ s') a. 29.4 m/s b. 88.2 m/s c, 265 m/s2 d. 3.27 m/s 18. If the a net torque is applied to an object, that object will experience: a. a constant angular speed b. an angular acceleration. c. A constant moment of incrtia d. An increasing moment of inertia 19. A disk has a moment of inertia of 3.0 x 10* kg*m2 and rotates with an angular speed of 3.5 rad/sec. What net torque must be applied to bring it to rest within 3 s? a. 4.5 x 10 N m b. 7.5 x 104 N m c. 3.5 x 10 N m d. 5.0 x 104 N m 20. A bowling ball has a mass of 7.0 kg, a moment of inertia of 2.8 x 10 kg'm2 and a radius of 0.10 m. If it rolls down the lane without slipping at a linear speed of 4.0 m/s, what is its total kinetic energy? a. 45 J b. 32J c. 11J d. 78J p. 5

Explanation / Answer

16- c ( angular acceleration is change in angular speed divided by time)

17-a (g = GM/R^2, M= density x volume, volume = 4/3*pi*R^3, g= 4/3*G*pi*densiry*R^3/R^2 = linear variation with Radius, if radius is tripled, g will also get tripled)

18-b (torque = Moment of intertia x angular momentum)

19-c ( angular acceleration= change in angular speed divided by time, torque= angular acceleration x moment of inertia)

20-d (total KE= linear + angular KE, linear KE= 1/2*m*v^2 where v is linear speed, angular KE = 1/2*Moment of inertia*angular speed^2, angular speed = linear speed/radius)

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