37 terms

# PHYSICS QUIZ #4

###### PLAY
1) Which of Newton's laws best explains why motorists should buckle-up?
A) the first law
2) When you sit on a chair, the resultant force on you is
A) zero.
3) In the absence of an external force, a moving object will
D) move with constant velocity.
4) When the rocket engines on the starship NO-PAIN-NO-GAIN are suddenly turned off, while
traveling in empty space, the starship will
D) move with constant speed.
5) A rocket moves through empty space in a straight line with constant speed. It is far from the
gravitational effect of any star or planet. Under these conditions, the force that must be
applied to the rocket in order to sustain its motion is
D) zero
6) You are standing in a moving bus, facing forward, and you suddenly fall forward. You can
imply from this that the bus's
A) velocity decreased.
7) You are standing in a moving bus, facing forward, and you suddenly fall forward as the bus
comes to an immediate stop. What force caused you to fall forward?
8) A constant net force acts on an object. Describe the motion of the object.
constant acceleration
The acceleration of an object is inversely proportional to
its mass
A net force F accelerates a mass m with an acceleration a. If the same net force is applied to
mass 2m, then the acceleration will be
a/2
A net force F acts on a mass m and produces an acceleration a. What acceleration results if a
net force 2F acts on mass 4m?
2a
If you blow up a balloon, and then release it, the balloon will fly away. This is an illustration
of
Newton's third law
Two cars collide head-on. At every moment during the collision, the magnitude of the force
the first car exerts on the second is exactly equal to the magnitude of the force the second car
exerts on the first. This is an example of
Newton's third law.
If you exert a force F on an object, the force which the object exerts on you will
D) always be F.
15) Action-reaction forces
D) always act on different objects.
16) Action-reaction forces are
B) equal in magnitude but point in opposite directions.
17) A 20-ton truck collides with a 1500-lb car and causes a lot of damage to the car. Since a lot of
damage is done on the car
B) the force on the truck is equal to the force on the car.
An object of mass m sits on a flat table. The Earth pulls on this object with force mg, which we
will call the action force. What is the reaction force?
D) The object pulling upward on the Earth with force mg.
19) A child's toy is suspended from the ceiling by means of a string. The Earth pulls downward
on the toy with its weight force of 8.0 N. If this is the "action force," what is the "reaction
force"?
D) The toy pulling upward on the Earth with an 8.0-N force.
20) A golf club hits a golf ball with a force of 2400 N. The golf ball hits the club with a force
B) exactly 2400 N.
21) Your bat hits the ball pitched to you with a 1500-N instantaneous force. The ball hits the bat
with an instantaneous force, whose magnitude is
C) exactly equal to 1500 N.
22) State Newton's three laws.
Newton's first law: Every object continues in its state of rest, or of uniform velocity in a
straight line, as long as no net force acts on it.
Newton's second law: The acceleration of an object is directly proportional to the net
force acting on it, and is inversely proportional to its mass. The direction of the
acceleration is in the direction of the net force acting on the object.
Newton's third law: Whenever one object exerts a force on a second object, the second
exerts an equal force in the opposite direction on the first.
23) Mass and weight
C) are two different quantities.
24) The acceleration due to gravity is lower on the Moon than on Earth. Which of the following is
true about the mass and weight of an astronaut on the Moon's surface, compared to Earth?
B) Mass is same, weight is less.
25) An example of a force which acts at a distance is
B) weight.
26) Who has a greater weight to mass ratio, a person weighing 400 N or a person weighing 600 N?
C) Neither; their ratios are the same.
27) A stone is thrown straight up. At the top of its path, the net force acting on it is
D) equal to its weight.
28) A 20-N weight and a 5.0-N weight are dropped simultaneously from the same height. Ignore
air resistance. Compare their accelerations.
D) They both accelerate at the same rate because they have the same weight to mass ratio.
30) An object of mass m is hanging by a string from the ceiling of an elevator. The elevator is
moving up at constant speed. What is the tension in the string?
B) exactly mg
31) An object of mass m is hanging by a string from the ceiling of an elevator. The elevator is
moving upward, but slowing down. What is the tension in the string?
A) less than mg
32) The force that keeps you from sliding on an icy sidewalk is
C) static friction.
33) It's more difficult to start moving a heavy carton from rest than it is to keep pushing it with
constant velocity, because
D) mk < ms.
34) A horizontal force accelerates a box from rest across a horizontal surface (friction is present) at
a constant rate. The experiment is repeated, and all conditions remain the same with the
exception that the horizontal force is doubled. What happens to the box's acceleration?
A) It increases to more than double its original value.
35) A packing crate slides down an inclined ramp at constant velocity. Thus we can deduce that
A) a frictional force is acting on it.
36) A block of mass M slides down a frictionless plane inclined at an angle q with the horizontal.
The normal reaction force exerted by the plane on the block is
C) Mg cos q.
37) A block of mass M slides down a frictionless plane inclined at an angle q with the horizontal.
The normal reaction force exerted by the plane on the block is directed
C) perpendicular to the plane.
38) A block of mass M slides down a frictionless plane inclined at an angle q with the horizontal.
The gravitational force is directed
D) toward the center of the Earth.