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
• Heather can apply a force of 72 N to a wagon
in which sits her little brother, Bryce. The
combined mass of Bryce and the wagon is 48
kg. If starting from rest, how much speed will
the wagon pick up after Heather has pushed
for 3 s?
Answer
• 4.5 m/s
Question
• A golf ball leaves a tee at a speed of 75 m/s. If
the ball has a mass of 0.05 kg and gains this
speed in 0.02 s, what is the average force of
impact of the club on the ball?
Answer
• 187.5 N
Question
• What is the pressure on a table when a 15-N
dictionary with a 0.05 m² cover lies flat on it?
Answer
• 300 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 50-kg crate
slides across a factory floor. Friction on the
sliding crate is 200 N. What is the crate’s
acceleration?
Answer
• - 4 m/s² in the direction opposite motion
Question
• What is the acceleration of a 20-kg container
of paint being pulled upward (not sideways)
with a force of 300 N?
Answer
• 5 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.
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