Lecture 22

Summary

Tangential and radial acceleration
Rotational kinematics
Rotational inertia

Today's joke

Bonus question Ch.09

Energy in rotation

rotational kinetic energy

Example #1

Example #2

Torque

definition, units
torque vectors applet

Example #3

I have not yet found HTML5 equivalents to these torque applets. Sorry!

Newton's second law

torque & rotation applet
net torque & acceleration applet

Example #4

Example #5

work
power

gc6 7.20
The force as a function of time on a 0.060 kg tennis ball is depicted. What is the velocity of the ball after being struck if it was at rest initially? force vs. time graph

A. 0.20 m/s
B. 2.0 m/s
C. 20 m/s
D. 200 m/s
Answer

pse6 10.66
The Earth's rotation slows and its rotational period increases about 10 µs each year because tidal friction converts its kinetic energy into thermal energy. At what rate is energy removed to do this? Let M = 5.97×10²⁴ kg and R = 6.37×10⁶ m.
A. 357 kW
B. 65.8 MW
C. 522 GW
D. 1.88 TW
Answer

sb5 10.24
The center of mass of a 3.80-cm-radius baseball moves at 38.0 m/s. The baseball spins with angular speed 125 rad/s. What is the ratio of its translational to rotational kinetic energy, K_trans/K_rot?
A. 160
B. 96
C. 4.21
D. 0.10
Answer

PoP5 10.22
Referring to the figure below, what is the torque exerted by the fish about an axis perpendicular to the screen and passing through the fisherman's hand?
A. 168 N·m
B. 109 N·m
C. 200 N·m
D. 308 N·m

Answer

PoP5 10.41
A 0.500-m radius, 100-kg potter's wheel freely rotates at 50.0 rev/min. The potter can stop the wheel in 6.00 s by pressing a wet rag against the rim and exerting a radially inward force of 70.0 N. Find the effective coefficient of kinetic friction μ_k between wheel and rag.
A. 0.156
B. 0.227
C. 0.312
D. 0.533
Answer

sb5 10.46
A constant 25.0-N·m torque is applied to a grindstone with a moment of inertia I = 0.130 kg·m². Use energy principles to find the final angular speed ω_f of the grindstone after 15.0 revolutions.
A. 36.2 rad/s
B. 236 rad/s
C. 613 rad/s
D. 190 rad/s
Answer

force vs. time graph

C. 20 m/s

answer

D. 1.88 TW
solution equation

answer

A. 160
solution equation

answer

A. 168 N·m

answer

C. 0.312

answer

D. 190 rad/s