Physics Chapter 4
A car by itself is capable of a certain maximum acceleration. When it tows a car of the same mass, its maximum acceleration is
1/2
A push on a 1-kg brick accelerates it. Neglecting friction, equally accelerating a 10-kg brick requires
10x as much force
The mass of a lamb that weights 110 N is about
11kg
Vide: a pulley system with 2 18N blocks on each end. The scale reads 18N when the blocks are not accelerating. Consider the video tutorial you just watched. Suppose that we duplicate this experimental setup in an elevator. What will the spring scale read if the elevator is moving upward at constant speed?
18N Since the elevator is not accelerating, the reading on the scale is the same as in the video.
A car has a mass of 1000 kg and accelerates at 2 m/s2. What net force is exerted on the car?
2000N
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/s2
A 500-N parachutist opens his chute and experiences an air resistance force of 800 N. The net force on the parachutist is then
300N upwards
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
30m/s
If you are driving at 20 m/s and slam on your brakes and skid at 0.5g to a full stop, the skidding time is about
4s
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
Free fall is motion in which gravity is the only force acting. Is a skydiver who has reached terminal speed in free fall?
No
If a motorcycle moves with a constant acceleration, can you conclude that there is no net force acting on it?
No
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.
If the net force acting on a sliding block is somehow tripled, what happens to the acceleration?
The acceleration triples.
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
If an objects mass is decreasing while a constant force is applied to the object, the acceleration
increases
In considering proportions, acceleration is _______. inversely proportional to mass squared. equal to the product of force and mass. inversely proportional to mass. directly proportional to mass.
inversely proportional to mass.
Air resistance on a parachutist at terminal speed _______.
is greater for a heavier person
Two tennis balls fall through the air from a tall building. One of them is filled with lead pellets. The ball to reach the ground first is the
lead-filled
A massive block is being pulled along a horizontal frictionless surface by a constant horizontal force. The block must be __________.
moving with a constant nonzero acceleration
is a nonzero net force required for motion
no, example a car moving at constant speed
Two factors that greatly affect air resistance on falling objects are frontal area and
speed
Your weight as measured on your bathroom scale is
the force due to gravity on you
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.
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
air resistance during free fall depends on what two things
the speed and mass of the object
is a nonzero net force required for acceleration
yes
When a falling object has reached its terminal velocity, its acceleration is
zero
Recall Galileo's Leaning Tower experiment. With negligible air resistance, a heavy and a light object fall with the same increases in speed. with equal accelerations. to the ground in equal times. all of the above
all of the above
Compared to a 1-kg block of solid iron, a 2-kg block of solid iron has twice as much
all of these (mass, inertia, volume)
At equilibrium on a bathroom weighting scale, the downward pull of gravity on you is balanced by
an upward support force.
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
A sack of potatoes weighing 200 N falls from an airplane. As the velocity of fall increases, air resistance also increases. When air resistance equals 200 N, the sack's acceleration becomes
0 m/s2.
Two forces, of magnitude 4Nand 10N, are applied to an object. The relative direction of the forces is unknown. The net force acting on the object __________.
Cannot have a magnitude equa to 5N
You are dragging a block on a surface with friction at a steady speed of 2 m/s and exert a force of 5 N to do so. What is the force of friction? Why?
Equal to 5 N, because the force of friction should exactly balance out the force Dr. Hewitt applies, so that there is no net force acting on the block.
A block of mass 2kg is acted upon by two forces: 3N(directed to the left) and 4N(directed to the right). What can you say about the block's motion?
It could be moving to the left, moving to the right, or be instantaneously at rest
The mass of a rocket decreases as it burns through its fuel. If the rocket engine produces constant force (thrust), how does the acceleration of the rocket change over time?
It increases.
What general rule can you conclude about the force needed to keep an object in motion at a steady rate?
The force that you need to apply to keep an object moving at a steady rate is equal to the force resisting the motion of the object.
In the video, forces acting on the car that are parallel to the direction of motion are analyzed. How are these forces related?
The forces are equal in size, act in opposite directions, and produce a zero net force.
An object at rest cannot remain at rest unless which of the following holds?
The net force acting on it is zero. (If the body is at rest and the net force acting on it is zero, then it will remain at rest.)
If a block is moving to the left at a constant velocity, what can one conclude?
The net force applied to the block is zero. (If a body is moving with constant velocity, then it is not accelerating and the net force acting on it is zero.)
What happens to the weight reading on a scale you stand on when you toss a heavy object upward?
The scale reading will increase during the throw.
When does the proportion form of Newton's second law take the form of an equation?
When units of newtons and kilograms are used for force and mass
Is a satellite above the atmosphere that circles Earth in free fall?
Yes
If a motorcycle moves with a constant velocity, can you conclude that there is no net force acting on it?
Yes. Constant velocity means zero acceleration, so yes, no net force acts on the motorcycle.
Newton's second law relates an object's acceleration to its mass and the net force acting on it. Does Newton's second law apply to a situation in which there is no net force? Select the best explanation.
Yes. The law applies and it tells us that the object has constant velocity.
Ball 1 has less mass. Ball 2 has more mass. Both are dropped from the same height. Which ball has a greater acceleration as it drops toward the ground, and why?
both ball 1 and ball 2 have equal acceleration
If less horizontal force is applied to a sliding object than is needed to maintain a constant velocity, the object
eventually slides to a stop.
A large and a small person wish to parachute at equal terminal velocities. The larger person should
get a larger parachute