Ch. 6 Check Your Understanding Flashcards
Two forces F1 and F2 are acting on a box, causing the box to move across the floor. F1 comes from horizontal size, F2 comes from diagonal.
Which one of these statements is correct?
A) F2 does more work then F1 does
B) F1 does more work than F2 does
C) both forces do the same amount of work
D) neither force does any work
B
A box is being moved with a velocity v by a force P (in the same direction as v) along a level horizontal floor. The normal force is Fn, the kinetic frictional force is fk, and the weight is mg.
Which of the following statements is correct?
A) P does positive work, Fn and fk do zero work, and mg does negative work.
B) Fn does positive work, P and fk do zero work, and mg does negative work.
C) fk does positive work, Fn and mg do zero work, and P does negative work.
D) P does positive work, Fn and mg do zero work, and fk does negative work.
D
A force does positive work on a particle that has a displacement pointing in the +x direction. This same force does negative work on a particle that has a displacement pointing in the +y direction. In which quadrant of the x, y coordinate system does the force lie? A) first B) second C) third D) fourth
D
A suitcase is hanging straight down from your hand as you ride an escalator. Your hand exerts a force on the suitcase, and this force does work. This work is..
A) positive when you ride up and negative when you ride down
B) negative when you ride up and positive when you ride down
C) positive when you ride up or down
D) negative when your ride up or down
A
A sailboat is moving at a constant velocity. Is work being done by a net external force acting on the boat?
No
A ball has a speed of 15m/s. Only one external force acts on the ball. After this force acts, the speed of the ball is 7m/s.
Has the force done A) positive B) zero C) negative Work on the ball?
C
A rocket is at rest on the launch pad. When the rocket is launched, its kinetic energy increases. Consider all of the forces acting on the rocket during the launch, and decide whether the following statement is true or false:
The amount by which the kinetic energy of the rocket increases during the launch is equal to the work done by the force generated by the rockets engine.
False
A net external force acts on a particle that is moving along a straight line. This net force is not zero.
Which one of the following statements is correct?
A) the velocity, but not the kinetic energy, of the particle is changing
B) the kinetic energy, but not the velocity, of the particle is changing
C) both the velocity and the kinetic energy of the particle are changing
C
In a simulation on earth, an astronaut in his space suit climbs up a vertical ladder. On the moon, the same astronaut makes the exact same climb. Which one of the following statements correctly describes how the gravitational potential energy of the astronaut changes during the climb?
A) it changes by a greater amount on the earth
B) it changes by a greater amount on the moon
C) the change is the same in both cases
A
Suppose the total mechanical energy of an object is conserved. Which one or more of the following statements is/are true?
A) if the kinetic energy decreases, the gravitational potential energy increases
B) if the gravitational potential energy decreases, the kinetic energy increases
C) if the kinetic energy does not change, the gravitational potential energy also does not change
A, b, and c
The Kingda Ka roller coaster starts with a speed of 6.0 m/s at the top of the drop and attains a speed of 50.3 m/s when it reaches the bottom. If the roller coaster were then to start up an identical hill, what speed would it attain when it reached the top? Assume that friction and air resistance are absent.
Exactly 6.0 m/s
The drawing shows an empty fuel tank about to be released by three different jet planes. At the moment of release, each plane has the same speed, and each tank is at the same height above the ground. However, the directions of the velocities of the planes are different. Which tank has the largest speed upon hitting the ground? Ignore friction and air resistance.
Each tank hits the ground with the same speed
In which one or more of the following situations is the principle of conservation of mechanical energy obeyed?
A) an object moves uphill with an increasing speed
B) an object moves uphill with a decreasing speed
C) an object moves uphill with a constant speed
D) an object moves downhill with an increasing speed
E) an object moves downhill with a decreasing speed
F) an object moves downhill with a constant speed
B and D
A net external nonconservative force does positive work on a particle. Based solely on this information, you are justified in reaching only one of the following conclusions. Which one is it?
The total mechanical energy of the particle increases
In one case, a sports car, its engine running, is driven up a hill at a constant speed. In another case, a truck approaches a hill, and its driver turns off the engine at the bottom of the hill. The truck then coasts up the hill. Which vehicle is obeying the principle of conservation of mechanical energy?
Only the truck
Engine A has a greater power rating than engine B. Which one of the following statements correctly describes the abilities of these engines to do work?
Engines A and B can do the same amount of work, but engine A can do it more quickly.
Is it correct to conclude that one engine is doing twice the work that another is doing just because it is generating twice the power?
No
The same force F pushes in three different ways on a box moving with a velocity v. Rank the work done by the force F in ascending order (smallest first.)
A) force pushes from diagonal
B) force pushes from horizontal
C) force pushes from vertical
C, A, B
Consider the force F shown in the drawing. This force acts on an object that can move along the positive or negative x axis, or along the positive or negative y axis. The work done by this force is positive when the displacement of the object is along the ___ axis or along the ___ axis.
-x, +y
Two forces F1 and F2 act on a particle. As a result the speed of the particle increases. Which of the following is not possible?
The work done by each force is negative.
Force F1 acts on a particle and does work W1. Force F2 acts simultaneously on the particle and does work W2. The speed of the particle does not change. Which one of the following must be true? A) W1 is zero and W2 is positive B) W1 = -W2 C) W1 is positive and W2 is zero D) W1 is positive and W2 is positive
B) W1 = -W2
A person is riding on a Ferris wheel. When the wheel makes one complete turn, the net work done on the person by the gravitational force is ___.
Zero
In which of the following circumstances could mechanical energy not possibly be conserved, even if friction and air resistance are absent?
A) a car moves up a hill, it’s velocity continually decreasing along the way
B) a car moves down a hill, it’s velocity continually increasing along the way
C) a car moves along level ground at a constant velocity
D) a car moves up a hill at a constant velocity
D) A car moves up a hill at a constant velocity
A ball is fixed to the end of a string, which is attached to the ceiling at point P. As the drawing shows, the ball is projected downward at A with the launch speed v0. Traveling on a circular path, the ball comes to a halt at point B. What enables the ball to reach point B, which is above point A?
The balls initial kinetic energy
