Chapter 7 Concepts Physics

A 200-g mass attached to the end of a spring causes it to stretch 5.0 cm. If another 200-g mass is added to the spring, the potential energy of the spring will be A) 4 times as much B) 3 times as much C) twice as much D) the same E) sqrt(2) times as much

A

A 4-kg mass moving with speed 2 m/s and a 2-kg mass moving with a speed of 4 m/s are gliding over a horizontal frictionless surface. Both objects encounter the same horizontal force which directly opposes their motion, and are brought to rest by it. Which statement best describes their respective stopping distances? A) The 2-kg mass travels twice as far as the 4-kg mass before stopping B) The 2-kg mass travels further, but not necessarily twice as far C) The 4-kg mass loses more kinetic energy than the 2-kg mass D) Both masses travel the same distance before stopping E) The 4-kg mass travels twice as far as the 2-kg mass before stopping

A

In Fig 5-2, showing a pendulum, at what position is the kinetic energy maximum? A) A B) B C) C

A

Work done by static friction is always A) positive B) along the surface C) perpendicular to the surface D) zero E) Negative

D

Is it possible for a system to have negative potential energy? A) Yes, since the choice of the zero potential energy is arbitrary B) No, because this would have no physical meaning C) Yes, as long as the total energy is negative D) Yes, as long as the total energy is positive E) No, because the kinetic energy of a system must equal its potential energy

A

King Kong falls from the top of the Empire State Building, through the air (air friction is present), to the ground below. How does his kinetic energy (K) just before striking the ground compare to his potential energy (U) at the top of the building? A) K is less than U B) K is equal to U C) K is greater than U D) it it impossible to tell

A

A person carries a mass of 10 kg and walks along the +x-axis for a distance of 100m with a constant velocity of 2 m/s. What is the work done by this person? A) 20 J B) 0 J C) 200 J D) 1000 J E) None of the above

B

If both the mass and the velocity of a ball are tripled, the kinetic energy of the ball is increased by a factor of A) 18 B) 27 C) 6 D) 9 E) 81

B

The work energy theorem says A) the net work done minus the initial kinetic energy is the final kinetic energy B) the net work done plus the initial kinetic energy is the final kinetic energy C) the net work done is equal to the initial kinetic energy less the final energy D) final kinetic energy plus the net work done is the initial kinetic energy E) the net work done plus the final kinetic energy is the initial kinetic energy

B

To accelerate your car at a constant acceleration, the car's engine must A) develop ever-decreasing power B) maintain a constant power output C) maintain a constant turning speed D) develop ever-increasing power

B

You and your friend want to go to the top of the Eiffel Tower. Your friend takes the elevator straight up. You decide to walk up the spiral stairway, taking longer to do so. Compare the gravitational potential energy (U) of you and your friend, after you both reach the top, assuming that you and your friend have equal masses A) Your friend's U is greater than your U, because she got to the top faster B) Both of you have the same amount of potential energy C) It is impossible to tell, since the times and distances are unknown D) Your U is greater than your friend's U, because you traveled a greater distance in getting to the top

B

A leaf falls from a tree. Compare its kinetic energy K to its potential energy U. A) K increases, and U increases B) K decreases, and U increases C) K increases, and U decreases D) K and U remain constant E) K decreases, and U decreases

C

Car J moves twice as fast as car K, and car J has half the mass of car K. The kinetic energy of car J, compared to car K is A) 4^2:1 B) 4:1 C) 2:1 D) 1:2 E) the same

C

Compared to yesterday, you did 3 times the work in one-third the time. To do so, your power output must have been A) 3^4 times yesterday's power output B) the same as yesterday's power output C) 9 times yesterday's power output D) one-third of yesterday's power output E) 3 times yesterday's power output

C

If the net work done on an object is negative, then the object's kinetic energy A) remains the same B) is zero C) decreases D) increases E) cannot be determined without knowing the object's mass

C

In Fig 5-2, showing a pendulum, at what position is the potential energy maximum? A) A B) B C) C

C

A truck weighs twice as much as a car, and is moving at twice the speed of the car. Which statement is true about the truck's kinetic energy (K) compared to that of the car? A) The truck has twice the K of the car B) the truck has sqrt(2) times the K of the car C) All that can be said is that the truck has more K D) The truck has 8 times the K of the car E) The truck has 4 times the K of the car

D

If the net work done on an object is positive, then the object's kinetic energy A) decreases B) is zero C) remains the same D) increases E) cannot be determined without knowing the object's mass

D

If the net work done on an object is zero, then the object's kinetic energy A) decreases B) is zero C) increases D) remains the same E) cannot be determined without knowing the object's mass

D

Refer to Fig 5-3. If the radius of the loop is R, what vertical height does the ball rise to on the other side, neglecting friction? A) 2R B) R C) less than R D) greater than 2R

D

You throw a ball straight up. Compare the sign of the work done by gravity while the ball goes up with the sign of the work done by gravity while it goes down. A) Work up is +, and the work down is - B) Work up is -, and the work down is - C) Work up is +, and the work down is + D) Work up is -, and the work down is +

D

If you push twice as hard against a stationary brick wall, the amount of work you do A) doubles B) is cut in half C) quadruples D) remains constant but non-zero E) remains constant at zero

E

The total mechanical energy of a system A) is equally divided between kinetic energy and potential energy B) is constant only if nonconservative forces act C) is either all kinetic energy or all potential energy, at one instance D) can never be negative E) is constant only if conservative forces act

E

Two men, Joel and Jerry, push against a wall. Jerry stops after 10 min, while Joel is able to push for 5.0 min longer. Compare the work they do. A) Joel does 50% more work than Jerry B) Jerry does 50% more work than Joel C) Joel does 75% more work than Jerry D) Joel does 25% more work than Jerry E) Neither of them do any work

E

If the net work W done on an object is negative, the object's kinetic energy increases by an amount W (T/F)

F

Kinetic energy is proportional to speed (T/F)

F

Problems involving a non-conservative force cannot be solved because there is no definable potential energy (T/F)

F

The work required to stretch a spring changes linearly with the amount of stretch (T/F)

F

Work is a vector quantity (T/F)

F

A force can be exerted on an object and yet do no work (T/F)

T

If a force is directed perpendicular to the displacement, no work is done by that force (T/F)

T

If the net work W done on an object is positive, the object's kinetic energy increases by an amount W (T/F)

T

Kinetic energy is a scalar quantity (T/F)

T

Kinetic energy is proportional to mass (T/F)

T