Physics: Chapter 4
An apple weighs 1 N. When the apple is held at rest above your head, the net force on the apple is
0 N.
Scotty Skydiver of mass 100 kg experiences air resistance of 500 N, and an acceleration of about
0.5 g.
An apple at rest weighs 1 N. The net force on the apple when it is in free fall is
1 N.
The mass of a pet turtle that weighs 10 N is about
1 kg.
What is the weight of a 1-kilogram brick resting on a table?
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 rock is thrown vertically into the air. At the top of its path, its acceleration is
10 m/s^2
A 10-kg brick and a 1-kg apple are dropped in a vacuum. The force of gravity on the brick is
10 times more than the force on the apple
What is the net force acting on a 1-kg ball in free fall?
10.0 N
An object released from rest on another planet requires one second to fall a distance of 6 meters. What is the acceleration due to gravity on this planet?
12 m/s2
A tow truck exerts a force of 3000 N on a car, which then accelerates 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 net force is exerted on the car?
2000 N
A car traveling at 22 m/s comes to an abrupt halt in 0.1 second when it hits a tree. What is the deceleration of the car?
220 m/s^2
Calculate the weight in newtons of a 2300-kg elephant.
22540 2.3×10^4 N
What horizontally-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
Nellie pulls on a 10-kg wagon with a constant horizontal force of 30 N. If there are no other horizontal forces, what is the wagon's acceleration?
3.0 m/s2
A 2000-kg car experiences a braking force of 10,000 N and skids to a stop in 6 seconds. The speed of the car just before the brakes were applied was
30 m/s
A 500-N parachutist opens his chute and experiences an air resistance force of 800 N. The net force on the parachutist is then
300 N upward.
A 1000-kg automobile enters a freeway on-ramp at 20 m/s and accelerates uniformly up to 40 m/s in a time of 10 seconds. How far does the automobile travel during that time?
300 m
An astronaut on another planet drops a 1-kg rock from rest. The astronaut notices that the rock falls 2 meters straight down in one second. On this planet, how much does the rock weigh?
4 N
An astronaut on another planet drops a 1-kg rock from rest and finds that it falls a vertical distance of 2.5 meters in one second. On this planet, the rock has a weight of
5 N
A 10-kilogram block with an initial velocity of 10 m/s slides 10 meters across a horizontal surface and comes to rest. It takes the block 2 seconds to stop. The stopping force acting on the block is about
50 N
Suzie Skydiver, who weighs 500 N, reaches terminal velocity of 90 km/h. The air resistance on Suzie is then
500 N
Phil stands at rest with both feet on a scale that reads 500 N. When he gently lifts one foot, the scale reads
500N
A 10-N falling object encounters 4 N of air resistance. The net force on the object is
6 N.
A block is dragged without acceleration in a straight-line path across a level surface by a force of 6 N. What is the force of friction between the block and the surface?
6N
State Newton's second law of motion.
Acceleration is proportional to net force and inversely proportional to mass.
How does acceleration depend on the net force?
Acceleration is proportional to the net force.
In which case would you have the largest mass of gold? If your chunk of gold weighed 1 N on the
Moon.
Why does a heavy parachutist fall faster than a lighter parachutist who wears a parachute of the same size?
Terminal speed must be higher to make air drag equal the gravity force for a heavier person.
What is the acceleration of a falling object that has reached its terminal velocity?
The acceleration is 0
How does the direction of acceleration compare with the direction of the net force that produces it?
The acceleration is in the direction of the net force.
If the mass of a sliding block is tripled while a constant net force is applied, by how much does the acceleration change?
The acceleration is reduced to 1/3 of its original value.
When you push horizontally on a crate that doesn't slide on a level floor, how great is the force of friction on the crate?
The friction force is equal and opposite to your push.
A light woman and a heavy man jump from an airplane at the same time and open their same-size parachutes at the same time. Which person will get to the ground first?
The heavy man
A light woman and a heavy man jump from an airplane at the same time and open their same-size parachutes at the same time. Which person will get to a state of zero acceleration first?
The light woman
What is the net force that acts on a 10-N falling object when it encounters 4 N of air resistance? When it encounters10 N of air resistance?
The net forces are 6 N and 0 N, respectively.
Why doesn't a heavy object accelerate more than a light object when both are freely falling?
The ratio of the weight to mass is the same for all objects in the same locality.
What is the condition for an object experiencing free fall?
When gravity is the only force acting on an object, it is in free fall.
Once the crate is sliding, how hard do you push to keep it moving at constant velocity?
You push with a force equal to and opposite the dynamic friction force.
If more horizontal force is applied to a sliding object than is needed to maintain a constant velocity, the object
accelerates in the direction of the applied force
If an apple experiences a constant net force, it will have a constant speed.
acceleration.
If you double the net force on an object, you'll double its
acceleration.
force
any push or pull exerted on an object, measured in newtons ( or pounds in the british system)
Neglecting friction, a small and a large block of ice begin sliding down an incline together. The larger block reaches the bottom
at the same time as the small block.
Suppose a particle is being accelerated through space by a 10-N force. Suddenly the particle encounters a second force of 10 N in the opposite direction. The particle with both forces acting
continues at the speed it had when it encountered the second force.
Suzie Skydiver jumps from a high-flying plane. As her velocity of fall increases, her acceleration
decreases.
A coconut and a bird's feather fall from a tree through the air to the ground below. The force of air resistance is
greater on the coconut
A skydiver's terminal velocity will be greatest if she falls
head first.
Two objects of the same size, but unequal weights are dropped from a tall tower. Taking air resistance into consideration, the object to hit the ground first will be the
heavier object
As a skydiver gains speed in falling through the air, air resistance _______.
increases.
Air resistance on a parachutist at terminal speed _______.
is greater for a heavier person
A heavy block at rest is suspended by a vertical rope. When the block accelerates upward by the rope, the rope tension
is greater than its weight.
A skydiver steps from a helicopter and falls for a few seconds until terminal velocity is reached. Thereafter, until he opens his parachute, his acceleration
is zero.
Whenever the net force on an object is zero, its acceleration
is zero.
A single brick falls with acceleration g. The reason a double brick falls with the same acceleration is
its ratio of force to mass is the same.
A ball is thrown vertically into the air. Because of air resistance, its speed when it returns to its starting level compared with its initial speed is
less.
free fall
motion under the influence of gravitational pull only
An object's weight is properly expressed in units of
newtons.
A car by itself is capable of a certain maximum acceleration. When it tows a twice-as-massive car, its maximum acceleration is
one third
Two factors that greatly affect air resistance on falling objects are frontal area and
speed
terminal velocity
terminal speed with direction specified
newton
the SI unit of force. one newton (N) is the force that will give an object of mass 1 kg an acceleration of 1 m/s
newton's second law
the acceleration of an object is directly proportional to the net force acting on the object, is in the direction of the net force and is inversely proportional to the mass of the object
weight
the force upon an object due to gravity, mg ( more generally, the force that an object exerts on a means of support)
kilogram
the fundamental SI unit of mass. One kilogram (kg) is the mass of one liter ( 1 L) of water at 4 degrees celsius
A rock weighs 30 N on Earth and another rock weighs 30 N on the Moon. Which rock has the greater mass?
the one on the moon
mass
the quantity of matter in an object. more specifically, it is the measure of the inertia or sluggishness that an object exhibits in response to any effort made to start it, stop it, deflect it, or change in any way its state of motion
volume
the quantity of space an object occupies
friction
the resistive force that opposed the motion or attempted motion of an object either past another object with which is is in contact or through a fluid
A force of 1 N accelerates 1-kg box at the rate of 1 m/s2. The acceleration of a 2-kg box by a net force of 2 N is
the same.
terminal speed
the speed at which the acceleration of a falling object terminates because air resistance balances gravitational force
Recall Galileo's Leaning Tower experiment. With negligible air resistance, a heavy and a light object fall
to the ground in equal times. with equal accelerations. with the same increases in speed. all of the above
Whenever a net force acts on an object, there is a change in the object's _______.
velocity.
Compared to a 1-kg block of solid iron, a 2-kg block of solid iron has twice as much
volume. inertia. mass. all of the above
The force required to maintain a constant velocity for an astronaut in free space is equal to
zero
When a falling object has reached its terminal velocity, its acceleration is
zero
