Concept questions…forces & kinematics
Answers are now at the end.
1. If I drop a crumpled up piece of paper, its motion will be affected by air resistance as
well as gravity. Which of the following statements is true?
(a)
(b)
(c)
(d)
(e)
its speed will first increase and then decrease.
it will have a constant speed the whole way down.
it will have a constant acceleration that is less than 9.8 m/s2.
its acceleration will start out at 9.8 m/s2 but will decrease as the paper falls.
its acceleration will start at 9.8 m/s2 and will increase as the paper falls.
2. Which of the following has a net force of zero acting on it (i.e., no net force)?
(a)
(b)
(c)
(d)
(e)
the moon in its circular orbit.
a car moving at 30 m/s in a straight line.
a diver diving into a swimming pool.
a ball rolling down an inclined board.
a car slowing to a stop.
3. Explain how action-reaction is responsible for the motion of a rowboat. Choose the
best answer.
(a)
(b)
(c)
(d)
(e)
Oars push backward on water, water pushes boat forward.
Boat pushes water, water pushes boat.
Oars push forward on water, water pushes forward on oars.
Oars push backward on water, water pushes forward on oars.
Your arms pull back on oars, oars push forward on water.
4. Imagine a head-on collision between a large truck and a small compact car. During
the collision,
(a) the truck exerts a greater amount of force on the car than the car exerts on the truck.
(b) the car exerts a greater amount of force on the truck than the truck exerts on the car.
(c) neither exerts a force on the other; the car gets smashed simply because it gets in the
way of the truck.
(d) the truck exerts a force on the car but the car doesn’t exert a force on the truck.
(e) the truck exerts the same amount of force on the car as the car exerts on the truck.
5. A golf ball driven down the fairway travels through the air with a trajectory similar to
that shown below. Which force(s) is (are) acting on the golf ball during its entire flight?
Refer to I,II,III below, and select your answer from choices a,b,c,d,e.
I. the force of gravity
II. the force of the “hit”
III. the force of air resistance
(a) III only
(b) I and II
(c) I, II, and III
(d) I and III
(e) II and III
6. My nephew, who weighs ½ as much as me, sits on an office chair (one with wheels).
I sit on an identical chair and push him away with my feet. Assuming no friction, how
does his acceleration compare to mine during the time that I am pushing?
(a) Both are zero
(c) His is not zero, but mine is.
(e) His acceleration is ½ mine.
(b) They are not zero, and are identical
(d) His acceleration is twice mine
7. Two metal balls are the same size, but one weighs about twice as much as the other.
If these two are dropped from the roof of Gallalee Hall, the time they take to reach the
ground will be:
(a)
(b)
(c)
(d)
(e)
about half as long for the heavier ball.
about half as long for the lighter ball.
about the same time for both balls.
considerably less for the heavier ball, but not necessarily half as long.
considerably less for the lighter ball, but not necessarily half as long.
8. A book rests on a horizontal table. The support force exerted on the book by the table
is
(a) equal to the weight of the book.
(b) zero.
(c) greater than the weight of the book.
(d) less than the weight of the book (but not zero).
9. When you drive your car in a circle at a constant speed, what direction does the force
of friction on your tires point?
(a ) There is none
(b) In the direction you are driving
(c) Away from the center of the circle
(d) Toward the center of the circle
(d) In the direction opposite to the direction you are driving.
10. Which of the following is not a force?
(a)
(b)
(c)
(d)
(e)
gravity
friction
inertia
tension
…all of these are forces.
11. I push a large crate across the floor, exerting a force F on the crate. There is friction
between the floor and the crate. The force the crate exerts on me is
(a)
(b)
(c)
(d)
zero
F
greater than F
less than F (but not zero)
12. Consider the Atwood’s machine shown. Given that m2 > m1, it follows that the
tension force in the string satisfies which of these relations (when the objects are
moving)?
m1
m2
(a) T > m2g > m1g
(e) m2g > T > m1g
(b) m2g > m1g > T
Clicker questions…energy
(c) T = m2g
(d) T = m1g
13. A cart initially at rest is allowed to roll down a frictionless ramp and attains a speed v
at the bottom. To achieve a speed 2v at the bottom, how many times as high must a new
ramp be?
(a) 1 (b) 2
(c) 3
(d) 4
(e) 1.414
14. A book sliding along a table slows down and stops. At first, the book had kinetic
energy; what has happened to this kinetic energy?
(a)
(b)
(c)
(d)
It was destroyed.
It became heat energy.
It became potential energy.
It became the kinetic energy of the table.
15. At which point on the roller coaster ride does the car have the greatest potential
energy, or (e) is it the same at all points?
a
c
b
d
16. If a car going 30 mph can stop in 100 feet, how much distance does the same car
require if stopping from a speed of 60 mph?
(a) 100 feet
Answers:
1d
2b
3d
4e
(b) 200 feet
(c) 300 feet
(d) 400 feet
(e) 800 feet
5d
6d
7c
8a
9d (actually, the force of friction is partly in the direction of motion, and partly toward
the center)
10c
11b
12e
13d
14b
15a
16d