AP Physics 1 and AP Physics C - Mechanics Daily Review: Fundamentals check 12

Major league baseball has installed a pitch clock.  Halleluiah!  I've complained about the length of baseball games for decades.  And finally, baseball has (with oh too much whining and complaining, from players and media members alike) addressed my concerns.  Most games are finishing well under three hours now, with many taking under 2.5 hours.  Yay.  I'm watching and listening to baseball again.

What does a pitch clock have to do with physics teaching?  Time is the currency of school.  I get 85 minutes with my AP class tomorrow - those 85 minutes are precious.  Yes, learning physics takes time!  And much of that time must be unstructured, time for discovery, time for lab play, time for arguing about physics, time for relationships to develop.  

Baseball takes time, too.  The new rules have adjusted the use of that time.  We used to get 60 minutes of action, 30 minutes of commercials, and 90 minutes of men scratching themselves, adjusting their batting gloves, contemplating, shaking off signs, and having committee meetings.  The new rules have reduced the 90 minutes of scratching etc. to more like 30 minutes per game.  And thus the action takes center stage, as it should.

In my classes, I regularly put up a countdown clock on the screen.  This counts down the time for quizzes and tests, yes, but also for a collaborative assignment, for acquisition of lab data, etc.  The clock isn't active every moment of class; but when it is, students know how much time they have to finish one activity and move on.  It's amazing how much more urgent and focused their behavior is when they see that timer.  Time waits for no one.  Just like batters figured out that they might not actually need to readjust their gloves after every pitch, students figure out for themselves what aspects of class are important and what aspects aren't.  

FUNDAMENTALS CHECK #12

111. Write the equation relating angular momentum to torque.

112. How do you find acceleration from a velocity-time graph?

113. Give an example of an object that experiences nonzero acceleration, but is not speeding up.

114. Under what conditions is a system's momentum conserved?

115. Two people wearing ice skates are initially at rest.  They push off each other, and head off with different speeds.  Why do the two people have the same magnitude of momentum as each other after the push?

116. Write the equation for the force exerted by a spring.

117. Moses runs up a staircase; Pav, who has the same mass as Moses [Note that I edited this question after its original publication], walks up the same staircase.  Who uses more energy to reach the top of the stairs?  Who generates more power reaching the top of the stairs?

118. Satellite A is in low-earth orbit; satellite B orbits much farther from earth's surface.  Which has greater gravitational potential energy: the satellite A-earth system, or the satellite B-earth system?

119.  Under what conditions are the kinematics equations valid?

120.  A string pulls a block to the left while the block moves to the right.  Is the work done by the string on the block positive, negative, or zero?