Exam 2 Flashcards
A centripetal force always acts in a direction ____________ to an object’s velocity. For this reason,
a centripetal force always does ___________ work.
A. parallel / positive
B. perpendicular / negative
C. opposite / zero
D. perpendicular / zero
D. perpendicular / zero
If the moon were orbiting closer to the planet, its speed would have to be ____________ because the
gravitational force on it and its centripetal acceleration would both be ____________.
A. the same / the same
B. greater / greater
C. less / less
D. greater / less
B. greater / greater
Which force does negative work on a box traveling upward in an elevator?
A. gravity
B. normal force
C. Both A and B
D. none of these
A. gravity
Which of the following is a nonconservative force?
A. tension
B. spring force
C. gravity
D. None of the above
A. tension
For an object in uniform circular motion, the velocity is always ______________, the acceleration is
always _____________, and the net force is always _______________ .
A. toward the center / toward the center / zero
B. zero / toward the center / zero
C. tangent to the circle / zero / zero
D. tangent to the circle / toward the center / toward the center
D. tangent to the circle / toward the center / toward the center
The magnitude of the gravitational force the Earth exerts on the Sun is _________________ the
magnitude of the gravitational force the Sun exerts on the Earth.
A. less than
B. the same as
C. greater than
D. the Earth doesn’t exert a gravitational force on the Sun.
B. the same as
Which of the following is a conservative force?
A. normal force B. air resistance
C. gravity D. tension
C. gravity
Which force does positive work on a box sliding down a ramp?
A. gravity B. friction C. normal force D. none of these
A. gravity
Four identical baseballs are brought to the roof of a stadium. Ball A is dropped off the edge from
rest. Ball B is thrown upward with a speed of 5 m/s. Ball C is thrown horizontally with a speed of
5 m/s, and ball D is thrown downward with a speed of 5 m/s. Which ball has the slowest speed just
before it hits the ground? (Ignore air resistance.)
A. ball A B. ball B C. ball C D. ball D
A. ball A
Which of the following exerts the greatest (magnitude) impulse on a tennis racket?
A. a 60-g tennis ball that starts from rest, is hit by the racket, and moves away at + 25 m/s
B. a 60-g tennis ball that approaches the racket at −25 m/s, is hit, and moves away at +25 m/s
C. a 60-g lump of clay that approaches the racket at −25 m/s, is hit, and sticks to the racket
D. The impulse is the same for all of these.
B. a 60-g tennis ball that approaches the racket at −25 m/s, is hit, and moves away at +25 m/s
- If no external forces act on two objects during a collision, momentum is conserved
A. only if one object starts at rest.
B. only if the objects bounce.
C. only if kinetic energy is conserved.
D. always.
D. always.
Now consider a (one-dimensional, i.e. head-on) collision between two identical billiard balls.
Before the collision, ball A’s velocity is + 2.0 m/s, and ball B is at rest. After the collision, ball B’s
velocity is + 2.0 m/s, and ball A is at rest. Taking the “system” to be the two billiard balls, which of
the following is true about the collision?
A. the collision is elastic
B. the collision is inelastic
C. momentum is not conserved
D. kinetic energy is not conserved
A. the collision is elastic
The Earth exerts a gravitational force on the International Space Station that keeps it in orbit. The
work done by this force is ___________ because it is ____________ to the space station’s velocity.
A. positive / parallel
B. zero / perpendicular
C. zero / opposite
D. negative / perpendicular
B. zero / perpendicular
Which force does positive work on a box traveling upward in an elevator?
A. gravity
B. normal force
C. Both A and B
D. none of these
B. normal force
Which of the following is a nonconservative force?
A. gravity
B. spring force
C. normal force
D. None of the above
C. normal force
