Physics

Can work be done on a system if there is no motion?

A) Yes, if an outside force is provided.

B) Yes, since motion is only relative.

C) No, since a system which is not moving has no energy.

D) No, because of the way work is defined.

D) No, because of the way work is defined.

Does the centripetal force acting on an object do work on the object?

A) Yes, since a force acts and the object moves, and work is force times distance.

B) Yes, since it takes energy to turn an object.

C) No, because the object has constant speed.

D) No, because the force and the displacement of the object are perpendicular.

D) No, because the force and the displacement of the object are perpendicular.

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 is + on the way up and + on the way down.

B) Work is + on the way up and - on the way down.

C) Work is - on the way up and + on the way down.

D) Work is - on the way up and - on the way down.

C) Work is - on the way up and + on the way down.

The area under the curve, on a Force versus position (F vs. x) graph, represents

      (Let the curve be a horizontal straight line)

A) work.

B) kinetic energy.

C) power.

D) potential energy

A) work.

The quantity 1/2 mv² is

A) the kinetic energy of the object.

B) the potential energy of the object.

C) the work done on the object by the force.

D) the power supplied to the object by the force.

A) the kinetic energy of the object.

The quantity mgy OR mgh is

A) the kinetic energy of the object.

B) the gravitational potential energy of the object.

C) the work done on the object by the force.

D) the power supplied to the object by the force.

B) the gravitational potential energy of the object.

State the work-energy principle

The work done on an object is equal to the change in its kinetic energy.

 The quantity 1/2 kx² is

A) the kinetic energy of the object.

B) the elastic potential energy of the object.

C) the work done on the object by the force.

D) the power supplied to the object by the force.

B) the elastic potential energy of the object.

The total mechanical energy of a system (PE + KE)

A) is equally divided between kinetic energy and potential energy.

B) is either all kinetic energy or all potential energy, at any one instant.

C) can never be negative.

D) is constant, only if conservative forces act. (like gravity)

D) is constant, only if conservative forces act.

An acorn falls from a tree.  Compare its kinetic energy K, to its potential energy U.

A) K increases and U decreases.

B) K decreases and U decreases.

C) K increases and U increases.

D) K decreases and U increases.

A) K increases and U decreases.

 An object is lifted vertically 2.0 m and held there.  If the object weighs 90 N, how much work was done in lifting it?

A) 360 J

B) 180 J

C) 90 J

D) 0 J

A) 180 J

 A 500-kg elevator is pulled upward with a constant force of 5500 N for a distance of 50.0 m.  What is the work done by the 5500 N force?

A) 2.75 × 10⁵ J

B) -2.45 × 10⁵ J

C) 3.00 × 10⁴ J

D) -5.20 × 10⁵ J

A) 2.75 × 105 J

Matthew pulls his little sister Sarah in a sled on an icy surface (assume no friction), with a force of 60.0 N at an angle of 37.0° upward from the horizontal.  If he pulls her a distance of 12.0 m, what is the work done by Matthew?

A) 185 J

B) 433 J

C) 575 J

D) 720 J

B) 433 J

 A horizontal force of 200 N is applied to move a 55-kg cart (initially at rest) across a 10 m level surface.  What is the final speed of the cart?

A) 73 m/s

B) 36 m/s

C) 8.5 m/s

D) 6.0 m/s

C) 8.5 m/s

 A spring is characterized by a spring constant of 60 N/m.  How much potential energy does it store, when stretched by 1.0 cm?    

A) 3.0 × 10^-3 J

B) 0.30 J

C) 60 J

D) 600 J

A) 3.0 × 10-3 J

A 60-kg mass skier starts from rest from the top of a 50-m high slope.  What is the speed of the skier on reaching the bottom of the slope? (Neglect friction.)

A) 22 m/s

B) 31 m/s

C) 9.8 m/s

D) 41 m/s

B) 31 m/s

 A driver, traveling at 22 m/s, slows down her 2000 kg car to stop for a red light.  What work is done by the friction force against the wheels?

A) -2.2 × 10⁴ J

B) -4.4 × 10⁴ J

C) -4.84 × 10⁵ J

D) -9.68 × 10⁵ J

C) -4.84 × 10⁵ J

At what rate is a 60.0-kg boy using energy when he runs up a flight of stairs 10.0-m high, in 8.00 s? (OR WHAT IS THE POWER?)

A) 75.0 W

B) 735 W

C) 4.80 kW

D) 48 W

B) 735 W

How many joules of energy are used by a 1.0 hp motor that runs for 1.0 hr? (1 hp = 746 W)

A) 3.6 × 10³ J

B) 2.7 × 10⁶ J

C) 4.5 × 10⁴ J

D) 4.8 J

B) 2.7 × 106 J

A roller coaster starts from rest at a point 45 m above the bottom of a dip (See Fig. above).  Neglect friction, what will be the speed of the roller coaster at the top of the next slope, which is 30 m above the bottom of the dip?

A) 14 m/s

B) 17 m/s

C) 24 m/s

D) 30 m/s

B) 17 m/s

List the six main forms of energy

Mechanical, thermal, chemical, electrical, nuclear, and radiant energy.

Coal, oil, and natural gas are fossil fuels. They are called fossil fuels  

    because

(a) they are burned to release energy and they cause air pollution

(b) they are formed from the buried remains of plants and tiny animals that 

     lived  hundreds of millions of years ago

(c) they are renewable

(d) they are mixed with fossil fuel to provide energy

(b) they are formed from the buried remains of plants and tiny animals that lived hundreds of millions of years ago.

 Solar, biomass, geothermal, wind and hydropower energy are all  

   renewable sources of energy. They are called renewable because they

(a) are clean and free to use

(b) can be converted directly into heat and electricity

(c) can be replenished by nature in a short period of time

(d) do not produce air pollution

(c) can be replenished by nature in a short period of time.