Physics Chapter 7

the energy associated with the motion of an object

kinetic energy

If the force is perpendicular to the motion , then W =

0

For each of two objects with different masses, the gravitational potential energy is 100 J. They are released from rest and fall to the ground. Which of the following statements is or are true. A. Both objects are released from the same height B.Both objects will have the same kinetic energy when they reach the ground C.Both objects will have the same speed when they reach the ground D. Both objects will accelerate toward the ground at the same rate

Both objects will have the same kinetic energy when they reach the ground Both objects will accelerate toward the ground at the same rate

Two identical objects are pressed against two different springs so that each spring stores 55.0J of potential energy. The objects are then released from rest. One spring is quite stiff (hard to compress), while the other one is quite flexible (easy to compress). Which of the following statements is or are true? (More than one statement may be true.) A. Both objects will have the same maximum speed after being released.B. The object pressed against the stiff spring will gain more kinetic energy than the other object.C. Both springs are initially compressed by the same amount.D. The stiff spring has a larger spring constant than the flexible spring.E. The flexible spring must have been compressed more than the stiff spring.

Both objects will have the same maximum speed after being released, the stiff spring has a larger spring constant than the flexible spring, and the flexible spring must have been compressed more than the stiff spring.

Three cars (car L, car M, and car N) are moving with the same velocity, and slam on the brakes. The most massive car is car L, and the least massive is car N. Assuming all three cars have identical tires, for which car is the amount of work done by friction in stopping it the highest?

Car L

A truck drives slams on the brakes of a moving truck with a constant velocity v, as a result of his action the truck stops after traveling a distance d. If the driver had been traveling with twice the velocity, what would be the stopping distance compared to the distance in the first trial? A. Two times greater B. Four times greater C. The same D. Half as much E. One-quarter as much

Four times greater

Two cyclists who weigh the same and have identical bicycles ride up the same mountain, both starting at the same time. Joe rides straight up the mountain, and Bob rides up the longer road that has a lower grade. Joe gets to the top before Bob. Which statement is true? Ignoring friction and wind resistance, the amount of work done by Joe is greater than the amount of work done by Bob, and the average power exerted by Joe is greater than that of Bob. Ignoring friction and wind resistance, the amount of work done by Joe is equal to the amount of work done by Bob, but the average power exerted by Joe is greater than that of Bob. Ignoring friction and wind resistance, the average power exerted by Bob and Joe was the same, but Joe exerted more work in getting there. Ignoring friction and wind resistance, Bob and Joe exerted the same amount of work, and the average power of each cyclist was also the same.

Ignoring friction and wind resistance, the amount of work done by Joe is equal to the amount of work done by Bob, but the average power exerted by Joe is greater than that of Bob.

What happens to the total energy of a moving object if all the applied forces are conserved? A. It increases B. It decreases C. It remains constant D. The velocity is required to answer this question E. The altitude is required to answer this question

It remains constant

You slam on the brakes of your car in a panic, and skid a certain distance on a straight, level road. If you had been traveling twice as fast, what distance would the car have skidded, under the same conditions? A) It would have skidded half as far. B) It woud have skidded twice as far. C) It would have skidded 4 times farther D) It would have skidded √2 times farther. E) It is impossible to tell from the information given.

It would have skidded 4 times farther

A bullet fired from a gun can pierce a target due to its a) Mechanical energy b) Heat energy c) Kinetic energy d) Acceleration

Kinetic energy

When a body slides against a rough horizontal surface, the work done by friction is a) Positive b) Zero c) Negative d) Constant

Negative

What happens to the kinetic energy of a moving object if the net work done is positive? A. The kinetic energy increases B. The kinetic energy decreases C. The kinetic energy remains the same D. The kinetic energy is zero E. The kinetic energy becomes negative

The kinetic energy increases

A girl throws a stone from a bridge. Consider the following ways she might throw the stone. The speed of the stone as it leaves her hand is the same in each case. Case A: Thrown straight up. Case B: Thrown straight down. Case C: Thrown out at an angle of 45° above horizontal. Case D: Thrown straight out horizontally.In which case will the speed of the stone be greatest when it hits the water below?

The speed will be the same in all cases

Three cars (car F, car G, and car H) are moving with the same velocity, and slam on the brakes. The most massive car is car F, and the least massive is car H. Assuming all three cars have identical tires, which car travels the longest distance to skid to a stop?

They all travel the same distance in stopping

An object I with a mass of 4 kg is lifted vertically 3 m from the ground level; another object II with a mass of 2 kg is lifted 6 m up. Which of the following statements is true? I. Object I has greater potential energy since it is heavier II. Object II has greater potential energy since it is lifted to a higher position III. Two objects have the same potential energy

Two objects have the same potential energy

An object is thrown straight up. Which of the following is true about the sign of work done by the gravitational force while the object moves up and then down? A. Work is positive on the way up, work is positive on the way down B. Work is negative on the way up, work is negative on the way down C. Work is negative on the way up, work is positive on the way down D. Work is positive on the way up, work is negative on the way down E. Work is zero the way up, work is zero on the way down

Work is negative on the way up, work is positive on the way down

When a car with its brakes locked skids across the pavenent with decreasing speed , the lost kinetic energy ______ be recovered by reversing the motion

cannot

A system in which the total mechanical energy, both kinetic and potential, is contant is called a

conservation system

When force = 0, the total mechanical energy is constant or __________

conserved

the total energy in any isolated system is _________, no matter what happens within the system

constant

Any force, such as friction, that turns mechanical enrgy into nonmechanical forms of energy is called a

dissipative force

energy that is stored in an elastic object when you sttetch, compress, twist, or otherwise deform it

elastic potential energy

The special case wehre a system has no interaction with its surrpundings

isolated system

When x increases, Work (elastic) is _______ and the stored enegy U(elastic) __________

negative; increases

If the force is perpendicular to the direction of displacement the force does ______ work on the object

no

When an object slides up and then back down to the starting point, the total work done on it by the friction force is ____ _______

not zero

When x decreases Work (elastic) is _______ and the stored enegy U(elastic) __________

positive; decreases

If the sign of the work is negative, then the force is _____ energy from the system or object

removing

The work of a conservative forces is always __________

reversible

W is a _____ quantity that can be positive, negative, or zero

scalar

the hotter an object, the more ________ its molecules vibrate

strongly

Conservative force are always be expressed as

the difference between the intiial and final values of a potential energy function

Two objects, one of mass m and the other of mass 2m, are dropped from the top of a building. When they hit the ground: both will have the same kinetic energy. the heavier one will have one-fourth the kinetic energy of the lighter one. the heavier one will have twice the kinetic energy of the lighter one. the heavier one will have half the kinetic energy of the lighter one. the heavier one will have four times the kinetic energy of the lighter one.

the heavier one will have twice the kinetic energy of the lighter one.

in any motion of a particle, the change in kinetic energy of the particle equals the ___ ____ done by the forces acting on it

total work

. A truck driver is trying to push a loaded truck with an applied force. Unfortunately, his attempt was unsuccessful the truck stays stationary no matter how hard the driver pushes. How much work is done by the driver?

zero

A construction worker holds a heavy tool box. How much work is done by the worker?

zero

A spacecraft moves around Earth in a circular orbit with a constant radius. How much work is done by the gravitational force on the spacecraft during one revolution?

zero

When the starting and ending points of a conservative force are the same the toal work is

zero

when an object slides along a surface, the work done by the normal force acting on the object is ________; when an object moves in a circle, the work done by the centripetal force on the object is also _______

zero; zero