Physics Chapter 7
interaction
features a pair of forces
pull/pull
force pair represented by vectors pointed away from each other
push/push
force pair represented by vectors pointed toward each other
push
force represented by the letter F
pull
force represented by the letter P
friction
force represented by the letter f
action
member of a force pair that acts in opposite direction as reaction
Fnet
resultant force (P-f, F-P, or F-f) that causes acceleration of a Horse-Cart system
force pair
rocket pushes exhaust gases, exhaust gases push rocket
system
the objects being considered in physics
second Law
F=ma
Earth pulls on the moon. Similarly, the moon pulls on Earth. We can say that
a) Earth and moon are pulling on each other. b) Earth's and moon's pulls are unequal. c) Earth pulls harder on the moon due to its larger mass. d) Earth pulls harder on the moon due to moon's smaller mass. ANSWER: A
A system undergoes acceleration only when acted on by
a) a pair of forces. b) action and reaction forces. c) internal interactions. d) a net force. ANSWER: D
A boulder falls due to gravity. The reaction force on the boulder is
a) air resistance. b) the boulder pulling up on Earth. c) the boulder being pulled downward by Earth. d) Earth pulling the boulder. ANSWER: B
When you jump vertically upward, strictly speaking, you cause Earth to
a) also move upward with you. b) remain stationary. c) move downward. d) move sideways a bit. ANSWER: C
When a cannonball is fired from a cannon, both the cannonball and the cannon experience equal
a) amounts of force. b) accelerations. c) changes in motion. d) increases in mass. ANSWER: A
A heavyweight boxing champion CANNOT hit a piece of tissue paper in midair with much force because
a) an interaction isn't possible in this case. b) the paper can't produce much opposite force. c) the paper is too light in weight. d) Newton's third law can't occur. ANSWER: B
The force that directly propels a vehicle along a highway is provided by the
a) engine. b) fuel. c)tires. d) road. ANSWER: D
The force that moves the horse-cart system is
a) friction by the ground on the horse's feet. b)reaction to the horse's pull on the wagon. c) reaction to the cart's pull on the horse. d) friction by the wheel of the cart on the ground. ANSWER: A
The force that propels a rocket is provided by
a) gravity b) Newton's laws of motion. c) its exhaust gases. d) the atmosphere against which the rocket pushes.
Whenever one object exerts a force on a second object, the second object exerts a force on the first that
a) is in the same direction. b) is equal in magnitude. c) occurs at slightly different times. d) satisfies Newton's laws. ANSWER: A
If a net force acts on a horse while it is pulling a wagon, the horse
a) is restrained. b) accelerates. c) is pulled backward by an equal and opposite net force. d) cannot move. ANSWER: B
When a squid pushes against water, the squid moves forward because
a) its tentacles apply a strong force to the water. b) its muscles flex. c) the water pushes against the squid. d) it swims using principles of flotation. ANSWER: C
A karate chop delivers a force of 3000 N to a board that breaks. The force that the board exerts on the hand during this event is
a) less than 3000 N. b) 3000 N. c) greater than 3000 N. d) impossible to tell from the information given. ANSWER: B
A force interaction involves
a) one force. b) two forces. c) just an action force. d) just a reaction force. ANSWER: B
How hard a boxer's punch lands depends mostly on the
a) physical condition of the boxer. b) mass of what's being hit. c) boxer's attitude. d) punching speed. ANSWER: B
The team that wins in a tug-of-war is the team that
a) produces more tension in the rope than the opponent. b) pushes hardest on the floor. c) pulls harder on the rope. d) lets the rope go slack, then pulls hard. ANSWER: B
The net force on a kicked football can be zero when it is kicked
a) so action and reaction both act on the ball. b) by two feet with equal and opposite amounts of force. c) by two feet in the same direction. d) by two feet at right angles to each other. ANSWER: B
When an air-filled balloon is untied and air escapes, the balloon shoots through the air. The force that propels the balloon is provided by the
a) surrounding air. b) ejected air. c) air still in the balloon. d) ground beneath the balloon. ANSWER: B
A massive truck and a golf cart have a head-on collision. A greater force acts on
a) the truck. b) the cart if it is initially at rest. c) the cart whether at rest or moving. d) neither, for both forces have the same magnitude. ANSWER: D
environment
everything in the universe except for the system
first Law
inertia:
third Law
interactions feature action and reaction forcese equal in magnitude, opposite in direction, and simultaneous in occurrence
a & m
variables that are inversely proportional to each other
cancellation
when a third object has opposing forces act upon it that have no resultant