Physics Exam 1
If a Mack truck and Honda Civic have a head-on collision upon which vehicle experiences a great deceleration
The Honda since the one with the smaller mass experiences a larger deceleration since a=F/m
Why are devices like seat belts and shoulder straps needed in automobiles
The body tends to keep its state of motion. So the body likes to continue to move forward. These devices prevent this forward motion.
A boxer can hit a heavy bag with a great force. Why can't he hit a piece of tissue paper in midair with the same amount of force
The force that the boxer applies to the tissue paper must be the same magnitude as the force that the tissue paper applies to the boxer which is a very small force.
When an object is thrown upward, how much speed does it lose each second
The object loses 9.8m/s^2 for a freely falling object
Identify the force that propels a rocket
The rocket's engine applies a force to the exploding gas (fuel) and pushes the gas molecules out of the engine compartment. According to the Newton's third law, the combination of all gas molecules apply a force of the same magnitude to the rocket in the opposite direction that propels the rocket.
A ball is tied to a string fastened at the other end to a rigid support forms a pendulum. If we pull the ball to one side and release it, the ball moves back and forth along an arc determined by the length of the string.
The speed and the velocity keep and changing and are not constant during the motion.
weight equation
W=mg
frictional force
a force that resists an object's movement
instantaneous velocity
a vector quantity having a size equal to the instantaneous speed at a given time and having a direction corresponding to that of the object's motion at that instant
acceleration equation
a= change in velocity/ elapsed time
Newton's first law of motion
an object remains at rest, or in uniform motion in a straight line, unless it is compelled to change by an externally imposed force
reaction force
an oppositely directed force in response to the initial force in an interaction governed by Newton's third law of motion
A heavy object and a light object are dropped from the same height and at the same time from rest in a vacuum. The heavier object reaches the ground:
at the same time as the lighter object
Why did Aristotle believe that heavier objects fall faster than lighter objects?
because a larger force acts on heavier objects
A ball is thrown downward with an initial velocity of 6 m/s. Another ball just dropped from the same height. Which ball has a larger acceleration? Assume negligible air resistance.
both have the same acceleration
A lead ball and an aluminum ball, each 1 inch in diameter, are released simultaneously from the same height, and allow to fall to the ground. Assume negligible air resistance. Which of these balls has a greater acceleration?
both have the same acceleration
A ball rolling rapidly along a tabletop rolls off the edge and falls to the floor. At the exact instant that the first ball rolls off the edge, a second ball is dropped from the same height. Which ball reaches the floor first?
both reach at the same time
Two identical pieces of paper, one crumpled into a ball and the other left uncrumpled, are released simultaneously from the same height falling through the air. Which one reaches the floor first? If the two pieces of the paper in the previous question are released inside a large evacuated tube, which one will reach the bottom of the tube first?
both reach the floor at the same time
average acceleration
change in velocity divided by the time required to produce that change
If an object falls with constant acceleration, the velocity of the object must: Be constant also.
continuously change by the same amount each second
distance equation
d=v0t + 1/2a(t^2)
the two measurements necessary for calculating average speed are
distance and time
average speed equation
distance traveled/ time of travel
speed
distance/time
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, the acceleration of:
each bullet is 9.8 m/s2
average speed
equals the distance traveled divided by the time of travel
reaction principle
for every action there is an equal but opposite reaction
the only way a net force can be 0 is
for the contributing forces Weight and Normal to cancel each other. They must be equal in magnitude and opposite in direction for their sum to be 0
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:
force the glove exerts on the ball
If an object falling freely downward were somehow equipped with an odometer to measure the distance it travels, then the amount of distance it travels each succeeding second would be:
greater than the second before
distance
how far an object travels
instantaneous speed
how fast an object is moving at a particular instant
speed
how fast something is moving
Newton's Third Law of motion
if object A exerts a force on object B, object B exerts a force on object A that is equal in magnitude but opposite in direction to the force exerted on b
suppose we choose inches as our basic unit of distance and days as our basic unit of time. What would the units of velocity be in this system?
in./day
suppose we choose inches as our basic unit of distance and days as our basic unit of time. What would the units of acceleration be in this system?
in./day^2
The tendency of objects to resist a change in motion is called:
inertia
what does the speedometer of a car measure?
instantaneous speed
velocity
involves the direction of motion as well as how fast the object is going
What does air resistance depend on
speed, and shape or area exposed to the air resistance, altitude
average speed
tells you how much distance a body covers during a certain time span
A cannonball fired at an angle of 70o to the horizontal stays in the air longer than one fired at 45o. Which one travels a longer horizontal distance?
the 45 degree ball
Newton's second law
the acceleration of an object is directly proportional to the magnitude of the imposed force and inversely proportional to the mass of the object. The acceleration is in the same direction as that of the imposed force
A ball is thrown straight upward and then returns to the ground. Does the acceleration change direction during this motion?
the acceleration of the ball is always directed downward throughout its flight
Two equal net forces act on two different objects, one of which has a mass ten times as large as the other. Compare the accelerations of the two objects?
the acceleration of the massive object is 1/10 the acceleration
A driver of a car steps on the brakes, causing the speed of the car to decrease. Does the car accelerate?
the car accelerates due to the change in its velocity
Two identical pieces of paper, one crumpled into a ball and the other left uncrumpled, are released simultaneously from the same height falling through the air. Which one reaches the floor first?
the crumpled piece
normal force
upward force always perpendicular to the surfaces of contact
velocity equation
v= initial velocity + acceleration(time)
A car traveling around a circular track moves with a constant speed of 100km/h. Is this car accelerating?
yes, because the direction of the velocity is changing
The force required to maintain a body at constant velocity in free space is equal to:
zero
A ball hangs from a ceiling and stays at rest as shown. What is the net force
0
1 lb = N
4.4
What does the coefficient g equal
9.8 m/s^2
What is the effect of air resistance on the acceleration of falling objects
Air resistance causes the object to have a smaller acceleration than falling without air resistance. As the object picks up speed, the air resistance increases, causing the downward acceleration to constantly decrease
What is the gain in speed per second for a freely falling object
For negligible air resistance the object falling near the surface of the earth will have an acceleration of 9.8m/s^2
When can acceleration be defined as the time rate of change of speed
In cases when direction does not change
Weight
Is the force of gravity (of the earth) acting on the object.
A freely falling body falls with a constant acceleration. Is the distance traveled by the body constant during each second?
NO, since the distance becomes progressively higher
IF a rock is transported from the earth to the moon, will either its mass or its weight change
its mass will remain the same, but its weight will become 1/6th of its weight on the earth
A ball is thrown straight upward. At the very top of its flight, which one of the following statements is correct?
its velocity is zero but its acceleration is not zero
A lead ball and an aluminum ball, each 1 inch in diameter, are released simultaneously from the same height, and allow to fall to the ground. Assume negligible air resistance. Which of these balls has a greater acceleration? Which one of the balls has a higher acceleration if air resistance is taken into account?
lead ball
A heavy man and a light man parachute together from a high-flying plane. The first man to attain zero acceleration will be the:
light man
Fnet=
ma
the inertia of an object is measured by its:
mass
Is the mass of an object the same thing as its weight?
mass is a measure of inertia or while weight is the gravitational force acting on an object
Did Galileo develop a more comprehensive theory of motion than that of Newton?
no, Newton's theory of motion is more comprehensive than that of Galileo
A car traveling around a circular track moves with a constant speed of 100km/h. Is this car moving with constant velocity
no, because the direction of motion of the car changes continuously
uniform acceleration
occurs whenever there is a constant force acting on an object
instantaneous speed
rate at which the distance is being covered at a give instant in time. IT is found by computing the average speed does not change appreciably.
What is the acceleration of a skydiver when air resistance builds up to be equal to her weight
she reaches terminal velocity
to specify a velocity we must give both its
size and direction
A rock is dropped from the top of a diving board into a swimming pool below. How does the distance traveled by the rock in a 0.1-second interval near the top of its flight compare to the distance covered in 0.1-second interval just before it hits the water?
the distance before it hits is larger
A car traveling in the forward direction experiences a negative acceleration for 10 seconds. Is the distance covered in the first 5 seconds equal to, greater than, or less than the distance traveled during the second 5 seconds?
the distance traveled during the first 5 seconds is greater than the second 5 seconds
A ball hangs from a ceiling and stays at rest as shown. What forces act on the ball?
the force of gravity and the string tension acting on the ball
air resistance
the frictional effects of the air or atmosphere on the motion of objects- especially noticeable on objects with large surface areas compared to their masses
A boy sits on the floor. What two vertical forces act on the boy?
the gravitation pull of the earth and the reaction force of the floor acting on the boy
weight
the gravitational force acting upon an object
A car is driven on a level surface. What force acting on the car is responsible for accelerating it forward?
the horizontal reaction force of the road on the car
Two identical cans, one filled with lead shots and one with feathers, are dropped from the same height. Which can experiences the greater force due to the gravity of the earth?
the lead can
mass
the measure of an object's inertia, the property that causes it to resist change in its motion
What is a freely falling object
the motion of the object is free of air resistance
terminal velocity
the point at which air resistance on a falling object equals the gravitational force, producing a net force of 0, which ends the object's acceleration. And the object will continue down at constant velocity.
acceleration
the rate at which velocity changes
instantaneous acceleration
the rate at which velocity is changing at a given instant in time. It is computed by finding the average acceleration for a very short time interval during which the acceleration does not change appreciably.
Inertia
the resistance against change of state. This means that objects tend to maintain their state of motion. In other words, if they are at rest, because of their inertia, they tend to stay at rest. If they are moving, then they tend to maintain the state of their motion.
Drop a rock from a 5-m height and it accelerates at 10 m/s2 and strikes the ground 1 s later. Drop the same rock from a height of 2.5 m and its acceleration of fall is:
the same
projectile motion
the trajectories and velocities of objects that have been launched, shot or thrown
acceleration due to gravity
the uniform acceleration of an object in a gravitational field 9.8m/s^2
A dropped ball gains speed at it falls. Can the velocity of the ball be constant in this motion?
the velocity is not constant because the speed is increasing
A football is thrown as a long pass. Consider the ball when it reaches the highest point on its path. Which of the following statements is correct?
the vertical component of the velocity is zero, but its horizontal component is not zero
At a given instant of time, two cars traveling at different speeds, one twice as large as the other. Based upon this information which car has the larger acceleration at this instant of time?
there is not enough information to determine the acceleration of the cars
If a Mack truck and Honda Civic have a head-on collision upon which vehicle is the impact force greater
they have the same force