physics exam three
A pool ball is rolling along a table with a constant velocity. The components of its velocity vector are vx=0.6m/s and vy=0.8m/s. Calculate the distance it travels in 0.3 s
0.30 m
Suppose that we attach Velcro® to the non-magnetic ends of the two carts in the video and remove the mass bars, so that both carts have the same mass. We repeat the experiment shown in the video, and the carts stick together after they collide. If the launch cart travels at a speed v0, then how fast will the combined two-cart system travel after the collision?
0.5v0 Linear momentum is conserved in this collision.The mass of the moving launch cart essentially doubles when it sticks to the target cart. Since the mass of the moving part of the system doubles, the speed must halve.
An airplane needs to reach a velocity of 186 km/h to take off. On a 2000 m runway, what is the minimum acceleration necessary for the plane to take flight?
0.67 m/s2
A car accelerates from 8 m/s to 23 m/s at a rate of 3.0 m/s2. How far does it travel while accelerating?
78 m
A football player kicks a football in a field goal attempt. When the football reaches its maximum height, what is the relationship between the direction of the velocity and acceleration vectors? Assume air resistance is negligible
At the maximum height, the velocity and acceleration vectors are perpendicular to each other.
Which of the following best describes how to calculate the average acceleration of any object?
Average acceleration is always equal to the change in velocity of an object divided by the time interval
An object is moving with constant velocity. Which of the following best describes the force(s) acting on the object?
No forces are acting on the object.
Person B does twice the work of person A, and in one-half of the time . How does the power output of person B compare to person A?
Person B has four times the power output of person A
The video shows an animated billiards experiment in which a cue ball strikes a glued-in-place eight-ball. Which of the following explains why the momentum of the eight-ball is conserved?
The "glue force" cancels the collision force During the collision, the force exerted by the glue (on the eight-ball) cancels the force exerted by the cue ball (on the eight-ball). Thus, the momentum of the eight-ball system is conserved because the net external force acting on it is zero.
true statements
The SI unit of power is the watt. Power is the rate at which energy is transformed. Power is the rate at which work is done. A person is limited in the total work he or she can do by the rate at which energy can be transformed.
A crate slides up an inclined ramp and then slides down the ramp after momentarily stopping near the top. This crate is acted upon by friction on the ramp and accelerates both ways
The acceleration going up the ramp is greater than the acceleration going down
The same net force is applied to two different objects. The second object has twice the mass of the first object. Compare the acceleration of the two objects
The acceleration of object 1 is twice the acceleration of object 2
The figure shows the velocity versus time graph for a car driving on a straight road. Which of the following best describes the acceleration of the car?
The acceleration of the car is positive and decreasing
A lump of putty and a rubber ball have equal mass. Both are thrown with equal speed against a wall. The putty sticks to the wall. The ball bounces back at nearly the same speed with which it hit the wall. Which object experiences the greater momentum change?
The ball experiences the greater momentum change
At what angle, above the horizon, should a cannon be fired in order for the cannon ball to obtain the greatest horizontal range? Assume air resistance is negligible
The cannon should be fired at an angle of 45° above the horizon
When a constant force acts on an object, what does the object's change in momentum depend upon?
The change in momentum depends upon the mass of the object. The change in momentum depends on the change in velocity of the object. The change in momentum depends on the magnitude of force. The change in momentum depends on the time interval during which the force acts.
A large truck collides head-on with a small car. The car is severely damaged as a result of the collision. According to Newton's third law, how do the forces acting between the truck and car compare during the collision?
The force on the truck is equal to the force on the car.
For general projectile motion, which of the following best describes the horizontal component of a projectile's acceleration? Assume air resistance is negligible
The horizontal component of a projectile's acceleration is zero
For a projectile launched horizontally, which of the following best describes the horizontal component of a projectile's velocity? Assume air resistance is negligible
The horizontal component of the projectile's velocity remains a nonzero constant
What represents the impulse of the force in a graph of force versus time?
The impulse is equal to the area under the curve.
In a lab environment, you are investigating the impulse of a force exerted on a brick when the brick's speed is reduced from 2.5 m/s to a complete stop. First, you allow the brick to slam into a secured piece of wood, bringing the brick to a sudden stop. Second, you allow the brick to plow into a large slab of gelatin so that the brick comes to a gradual halt. In which situation is there a greater impulse of the force on the brick?
The impulse is the same in both situations
A packing crate is sitting at rest on an inclined loading ramp. How does the magnitude of the force of static friction compare to the other forces acting on the crate?
The magnitude of the force of static friction is equal to the magnitude of the component of the weight of the crate parallel to the inclined ramp.
An object is hanging by a string from the ceiling of an elevator. The elevator is moving upward with a constant speed. What is the magnitude of the tension in the string?
The magnitude of the tension in the string is equal to the magnitude of the weight of the object.
An object is hanging by a string from the ceiling of an elevator. The elevator is slowing down while moving upward. What is the magnitude of the tension in the string?
The magnitude of the tension in the string is less than the magnitude of the weight of the object.
A person applies a 50 N force on a crate, causing it to move horizontally at a constant speed through a distance of 10 m. What is the net work done on the crate?
The net work done on the crate is zero joules. Since the object is at constant speed, its acceleration is 0. Net work is equal to mass times distance times acceleration; therefore the answer is 0.
A constant net force acts on an object. Which of the following best describes the object's motion?
The object is moving with a constant acceleration
If the net work done on an object is positive, what can you conclude about the object's motion?
The object is speeding up the positive work done increases the energy of the body, since work is equal to F . r thus f and r must be in the same direction, thus increasing the velocity of the body
Newtons second law: An object is moving in the absence of a net force. Which of the following best describes the object's motion?
The object will continue to move with a constant velocity
If the net work done on an object is zero, what can you determine about the object's kinetic energy?
The object's kinetic energy remains the same.
A pilot releases a package from a plane flying horizontally at a constant speed. When the package reaches the ground below, what is the horizontal location of the plane with respect to the package? Assume air resistance is negligible
The plane will be located directly above the package.
What shape do we expect for a graph showing the position of a motorcycle versus time if the motorcycle is speeding up with a constant acceleration?
The position versus time graph is parabolic.
A player kicks a soccer ball in a high arc toward the opponent's goal. When the soccer ball reaches its maximum height, how does its speed at this point compare to its initial speed? Assume air resistance is negligible
The speed at its highest point is less than its initial speed
A swimmer is determined to cross a river that flows due south with a strong current. Initially, the swimmer is on the west bank desiring to reach a camp directly across the river on the opposite bank. In which direction should the swimmer head?
The swimmer should swim northeast
the following statements are true.
The total mechanical energy of a system is constant only if conservative forces act. Mechanical energy can be dissipated to nonmechanical forms of energy.
When a person steps forward out of a small boat onto a dock, the boat recoils backward in the water. Why does this occur?
The total momentum of the system is conserved.
A red water balloon is thrown horizontally from the top of a bridge. At the same instant, a yellow water balloon is dropped off the bridge from the same height. Compare the time of fall for the two balloons. Assume air resistance is negligible
The two balloons hit the ground at the same time.
Two objects are moving at equal speed along a level, frictionless surface. The second object has twice the mass of the first object. They both slide up the same frictionless incline plane. Which object rises to a greater height?
The two objects rise to the same height. the formula in use is square root of 2gh
An object moves in a circular path at a constant speed. What is the relationship between the directions of the object's velocity and acceleration vectors?
The velocity and acceleration vectors are perpendicular
A red ball with a velocity of +3.0 m/s collides head-on with a yellow ball of equal mass moving with a velocity of −2.0 m/s. What is the velocity of the two balls after the elastic collision?
The velocity of the red ball is −2.0 m/s; the velocity of the yellow ball is +3.0 m/s.
For general projectile motion, which of the following best describes the vertical component of a projectile's acceleration? Assume air resistance is negligible
The vertical component of a projectile's acceleration remains a nonzero constant.
For a projectile launched horizontally, which of the following best describes the vertical component of a projectile's velocity? Assume air resistance is negligible
The vertical component of the projectile's velocity continually increases
velocity differs from speed in that velocity indicates a particle's __________ of motion.
direction
Speed differs from velocity in the same way that __________ differs from displacement
distance
A plastic ball in a liquid is acted upon by its weight and by a buoyant force. The weight of the ball is 6.7 N. The buoyant force has a magnitude of 9.4 N and acts vertically upward. At a given instant, the ball is released from rest. The acceleration of the ball at that instant, including direction, is closest to
first find the mass of the ball. (6.7/9.8) that mass times the acceleration (m *x)= Fb iddkkk answer: 3.9 m/s2 upward
Two balls are dropped from the top of the Leaning Tower of Pisa. The second ball is dropped a fraction of a second after the first ball. As they continue to accelerate to the ground, the distance between them will
increase
A vector has, by definition, both __________ and direction.
magnitude
A motorcycle drives up a steeply inclined ramp. The work done on the motorcycle by the Earth's gravitational force is ____.
negative When an object's displacement has a component in a direction opposite that of a given force, that force does negative work on the object.
Your boat departs from the bank of a river that has a swift current parallel to its banks.
perpendicular to the current.
Consider a physical situation in which a particle moves from point A to point B. This process is described from two coordinate systems that are identical except that they have different origins. The __________ of the particle at point A differ(s) as expressed in one coordinate system compared to the other, but the __________ from A to B is/are the same as expressed in both coordinate systems.
position, displacement
A freight car moves along a frictionless level railroad track at constant speed. The freight car is open on the top. A large load of sand is suddenly dumped into the freight car. What happens to the speed of the freight car?
speed of freight car decreases
Which statement must be true for the momentum of a system to be conserved?
the net external force of the system must be zero
An object is at rest on a tabletop. Earth pulls downward on this object with a force equal in magnitude to mg. If this force serves as the action force, what is the reaction force in the action-reaction pair?
the object pulling upward on Earth
During a certain time interval, the net work done on an object is zero joules. We can be certain that ____.
the object's final speed was the same as its initial speed
While goofing off at the ice skating rink, a student takes off her shoes and places each of them on the ice. Her friend, a hockey player, then shoots a hockey puck at each shoe. The first puck immediately comes to rest after it collides with the left shoe. The second puck rebounds after it collides with the right shoe. If each hockey puck has the same incoming speed, which shoe has greater speed after the collision?
the right shoe
Two identical cars are driving in opposite directions at the same speed. Their kinetic energies have ____.
the same magnitude and sign The kinetic energy of a moving object is always positive, regardless of the direction it is moving in, or the coordinate system used
true statements
the total momentum of an isolated system is constant C) the total momentum of any number of particles is equal to the vector sum of the momenta of individual particles D)The vector sum of forces acting on a particle equals the rate of change of momentum of the particle with respect to time
An object of weight W falls from rest subject to a frictional drag force bv2. What maximum ("terminal") velocity will it approach if W = 4 N and b = 3 N⋅s2/m?
v = 1.15 m/s Terminal velocity: net forces = 0 therefore the weight is equal to drag force solve for v.
Unlike speed, velocity is a __________ quantity.
vector
A graph depicts force versus position. What represents the work done by the force over the given displacement?
The work done is equal to the area under the curve.
An object weighing 20 N moves horizontally toward the right a distance of 5.0 m. What is the work done on the object by the force of gravity?
The work done on the object by the force of gravity is zero joules. Since gravity is perpendicular to the object, the net force is zero.
Once you have selected a coordinate system, you can express a two-dimensional vector using a pair of quantities known collectively as __________.
components
Consider what happens when you jump up in the air. Which of the following is the most accurate statement?
When you push down on the earth with a force greater than your weight, the earth will push back with the same magnitude force and thus propel you into the air
A ball is thrown straight upward. How does the sign of the work done by gravity while the ball is traveling upward compare with the sign of the work done by gravity while the ball is traveling downward?
Work done by gravity is negative while the ball is traveling upward and positive while the ball is traveling downward.
An elevator moves straight upward at a constant speed. Newton's first law predicts that the net force acting on the elevator will _____.
be zero
