Download Chapter 6, 7 - Standards Aligned System

Chapter 6, 7
Newton’s Second and Third Law
Question
• For a constant force, how does an increase in
mass affect an object’s acceleration?
Answer
• Decreases acceleration
Question
• What causes accelerations? Be as specific as
possible!
Answer
• A nonzero net force
• Unbalanced force
Question
• What quantity is directly proportional to an
object’s acceleration?
Answer
• Force
Question
• Calculate the acceleration of a 100-kg cart
when the net force on it is 50 N.
Answer
• A = 0.5 m/s²
Question
• Calculate the horizontal force needed to make
a 1-kg hockey puck accelerate at 1000 m/s²
Answer
• 1000 N
Question
• A 5.0 kg block accelerates at 0.80 m/s2 along a
horizontal surface when a horizontal 12.0 N
force acts on it. What is the force of friction?
Answer
• 8.0 N
Question
• What braking forces is needed for a truck of
mass 3,000 kg that is slowed from 32 m/s to
12 m/s in 6 s?
Answer
• -10,000 N
Question
• What is the pressure on a table when a 10-N
dictionary with a 0.07 m² cover lies flat on it?
Answer
• 143 N/m²
Question
• A 500-kg subcompact car and a 1500-kg
standard car are given equal accelerations.
How much greater is the force that acts on the
more massive car?
Answer
• The force on the big car is 3 times that on the
small car.
Question
• Scarlet Skydiver, who has a mass of 60 kg,
jumps form a stationary helicopter. What is
the net force on her 10 s into the dive, when
she has reached terminal speed?
Answer
• Net force = 0
Question
• What factors affect the force of friction
between surfaces? (2; 1 point each)
Answer
• Kinds of material in contact
• How much the surfaces are pressed together
(the support force)
Question
• After being pushed and released, a 67-kg crate
slides across a factory floor. Friction on the
sliding crate is 222 N. What is the crate’s
acceleration?
Answer
• - 3.3 m/s² in the direction opposite motion
Question
• What is the acceleration of a 15-kg cat being
pulled upward (not sideways) with a force of
120 N?
Answer
• 2 m/s²
Question
• A 10.0-kg block slides down a ramp inclined
30° to the horizontal. How great is the normal
force by the ramp on the block?
Answer
• 86.6 N
Question
• Find the acceleration of a plastic block of mass
3 kg that slides down a friction free plane
inclined at 42°to the horizontal.
Answer
• 6.7 m/s²
Question
• For a constant force, how does an increase in
area affect the resulting pressure?
Answer
• It decreases pressure
Question
• True or False: Gravity exerts a greater force on
more massive objects.
Answer
• True
Question
• What 2 factors affect the amount of air
resistance an object experiences? (1 point
each)
Answer
• Speed and area
Question
• The ratio of _____ to _____ is the same for all
objects. This proves that all objects
undergoing free fall (in the absence of air
resistance) will accelerate at the same rate.
Answer
• weight
Question
• Scarlet Skydiver, who has a mass of 60 kg,
jumps from a stationary helicopter. What is
her acceleration when she reaches terminal
speed?
Answer
• a = 0 m/s²
Question
• Mass and weight are proportional. This means
that heavier objects also are more massive. If
gravity pulls on heavier objects with a greater
force, how is it that all objects undergoing free
fall accelerate at the same rate in the absence
of air resistance?
Answer
• More massive objects have more inertia
Question
• When accounting for air resistance, which will
reach terminal speed first, a feather or a coin?
Answer
• A feather
Question
• For a constant area, how will an increase in
force affect the resulting pressure?
Answer
• Increase in pressure
Question
• A 5 kg box slides down an incline at an angle
of 15° to the horizontal. Find the coefficient of
friction between the box and the incline.
(Assume constant velocity)
Answer
• 0.27
Question
• A 65-kg astronaut in the space station kicks a
soccer ball with a force of 13 N. At what rate
does the astronaut accelerate backward?
Answer
• a = 0.20 m/s²
Question
• Daniel (mass 40 kg) and Justin (mass 60 kg)
face each other at rest while wearing roller
blades. Daniel pushes Justin and accelerates
him at 1.6 m/s². What is Daniel’s acceleration
in the other direction?
Answer
• 2.4 m/s²
Question
• Forces always occur in __________
Answer
• pairs
Question
• Consider hitting a baseball with a bat. If we
call the force the bat exerts against the ball
that action force, identify the reaction force.
Answer
• A baseball hits a bat
Question
• When a cannon is fired, why do the
cannonball and cannon have very different
accelerations?
Answer
• Because of their different masses
Question
• A small car bumps into a van at rest in a
parking lot. Upon which vehicle is the force of
impact greater?
Answer
• Neither; force is the same on each vehicle
Question
• A speeding bus makes contact with a bug that
splatters on the windshield. Because of the
sudden force, the unfortunate bug undergoes
a sudden deceleration. Is the resulting
deceleration of the bus greater than, less
than, or that same as that of the bug?
Answer
• Less than
Question
• Suppose you exert 200 N on your refrigerator
and push it across the kitchen floor at
constant velocity. Friction opposes your push
with 200 N of force as well. Does the friction
force make up the reaction force to your
push?
Answer
• No; the reaction to your push on the
refrigerator is the refrigerator’s push back on
you
Question
• 2 people attempt tug of war on low friction
ice. One person has 4 times the mass of the
other. Relative to the acceleration of the
heavier person, what will be the acceleration
of the lighter person?
Answer
• The lighter person will have 4 times the
acceleration of the heavier person.
Question
• Why don’t action-reaction forces cancel each
other out?
Answer
• Because one of the forces is external to the
system being considered.
Question
• Use Newton’s Third Law to explain how
rockets move forward.
Answer
• Rocket pushes gas backward; gas pushes
rocket forward