Exam 3 CH 3
A 10-N falling object encounters 10 N of air resistance. The net force on the object is
0 N.
A falling skydiver of mass 100 kg experiences 500-N air resistance. The acceleration of the skydiver is
0.5 g.
What net force does a sliding crate experience when you exert a force of 125N and the friction between the crate and floor is 115N?
10 N
A 1-kg ball is thrown at 10 m/s straight upward. Neglecting air resistance, the net force that acts on the ball when it is half way to the top of its path is about
10 N.
A 1-kg rock that weighs 10 N is thrown straight upward at 20 m/s. Neglecting air resistance, the net force that acts on it when it is half way to the top of its path is
10 N.
A baseball player bats a ball with a force of 1000 N. The ball exerts a reaction force against the bat of
1000 N.
A tow truck exerts a force of 3000 N on a car, accelerating it at 2 m/s2. What is the mass of the car?
1500 kg
A car has a mass of 1000 kg and accelerates at 2 m/s2. What is the magnitude of the force exerted on the car?
2000 N
A car traveling at 22 m/s comes to an abrupt halt in 0.1 s when it hits a tree. What is the deceleration in meters per second squared of the car?
220
What horizontal applied force will accelerate a 400-kg crate at 1 m/s2 across a factory floor against a friction force half its weight?
2400 N
An empty roller coaster car at an amusement park takes 3 min to make its ride from start to finish. Neglecting friction, a fully loaded car would take
3 min.
A 2000-kg car experiences a braking force of 10,000 N and skids to a stop in 6 s. The speed of the car just before the brakes were applied was
30 m/s.
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
3000 N
On the surface of Jupiter, where the acceleration due to gravity is about three times that of Earth, a 100-kg rock would have a weight of about
3000 N.
A person is attracted toward the center of Earth by a 500-N gravitational force. The force of attraction of Earth toward the person is
500 N.
A 10-N falling object encounters 4 N of air resistance. The magnitude of the net force on the object is
6 N.
Who falls faster when wearing the same-size parachute − a heavy person or a light person − or do both fall at the same speed?
A heavy person.
Do action and reaction forces act in succession or simultaneously?
Action and reaction forces act simultaneously.
What is needed to accelerate a system?
An external force.
You are dragging a block on a surface with friction at a steady speed of 2 m/s and exert a force of 5N to do so. What is the force of friction? Why?
Equal to 5N, because the force of friction should exactly balance out the force that you apply on a block, so that there is no net force acting on the block and you maintain a constant speed.
In the apple-pulling-the-orange system in this chapter, what is the force that accelerates the system across the floor?
Friction between the apple and the floor.
What test tells us whether or not a moving object is an equilibrium?
If the moving body doesn`t change its velocity, it is in equilibrium. If the body changes its velocity, it is not in equilibrium.
If the forces that act on a cannonball and the recoiling cannon from which it is fired are equal in magnitude, how does the acceleration of the cannonball compare with the acceleration of the cannon?
The acceleration of the cannonball is greater than the acceleration of the cannon due to small mass.
What is Newton's second law of motion?
The acceleration produced by a net force on an object is directly proportional to the net force, is in the same direction as the net force, and is inversely proportional to the mass of the object.
An object can not remain at rest unless which of the following holds?
The net force acting on it is zero.
What kind of path would the planets follow if suddenly their attraction to the Sun no longer existed?
The planets would move in straight-line paths.
When you push against a wall with your fingers, they bend because they experience a force. What is this force?
The push of the wall on you bends your fingers.
When you push against a wall, what pushes back?
The wall pushes back.
How many forces are required for a single interaction?
Two forces constitute a single interaction.
Why doesn't a heavy object accelerate more than a light object when both are freely falling?
When in free fall, the ratio of weight/mass is the same for all objects.
What is Newton's third law of motion?
Whenever one object exerts a force on a second object, the second object exerts an equal and opposite force on the first object.
Action and reaction forces comprise the parts of
a single interaction.
Your friend says that the heavyweight champion of the world cannot exert a force of 50 N on a piece of tissue paper with his best punch. The tissue paper is held in midair, no wall, no tricks. You
agree that it can't be done.
The amount of air resistance that acts on a wing suit flyer (and a flying squirrel) depends on the flyer`s
area and speed
A heavy object and a light object are dropped at the same time from rest in a vacuum. The heavier object reaches the ground
at the same time as the lighter object
Arnold Strongman and Suzie Small each pull very hard on opposite ends of a rope in a tug-of-war. The greatest force on the rope is exerted by
both the same, interestingly enough.
As mass is added to a pushed object, its acceleration
decreases
An object is propelled along a straight-line path by a force. If the net force were doubled, its acceleration would
double.
According to Newton's Law of Inertia, the result of walking around much of the day is similar to tightening the head of a hammer when its handle hits a solid surface so that we are actually a little bit shorter in the
evening.
Whirl a rock at the end of a string and it follows a circular path. If the string breaks, the tendency of the rock is to
follow a straight-line path.
A player hits a ball with a bat. The action force is the impact of the bat against the ball. The reaction to this force is the
force of the ball against the bat.
A player catches a ball. Consider the action force to be the impact of the ball against the player's glove. The reaction to this force is the
force the glove exerts on the ball.
As a skydiver gains speed in falling through the air, air resistance
increases.
If an object's mass is decreasing while a constant force is applied to the object, the acceleration
increases.
Newton's second law tells us that acceleration is
inversely proportional to mass.
The force that propels a rocket is provided by
its exhaust gases
A rock is thrown vertically into the air. At the very top of its trajectory, the net force on it is
its weight.
A ball thrown straight upward takes 10 s to go up and return to the ground. Because of air resistance, the time taken for the ball just to go up is
less than 5 s.
A force is a vector quantity because it has both
magnitude and direction.
A ball is thrown vertically into the air. Because of air resistance, its time coming down compared to its time going up is
more.
The force exerted on the tires of a car to directly accelerate it along a road is exerted by the
road.
A bullet is dropped from the top of the Empire State Building while another bullet is fired downward from the same location. Neglecting air resistance, acceleration is greatest for the
same for each
Can it be said that, when two vectors are at right angles to each other, the resultant is greater than either of the vectors separately?
yes
When a vector at an angle is resolved into horizontal and vertical components, can it be said that each component has less magnitude than the original vector?
yes
When you walk along a floor, you push against the floor. What pushes back?
The floor pushes you back
Consider hitting a baseball with a bat. If we call the force of the bat against the ball the action force, what is the reaction force?
The force of the ball against the bat.
A 1-kg stone and a 10-kg stone have the same acceleration in free fall, because
the ratio of weight to mass is the same for each.
