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# Stephen pulls David at constant speed upward along a frictionless water slide. - PowerPoint PPT Presentation

System. 40 o. Earth. Stephen pulls David at constant speed upward along a frictionless water slide. Which of the following statements best describes the situation?.

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40o

Earth

Stephen pulls David at constant speed upward along a frictionless water slide.

Which of the following statements best describes the situation?

1 The energy in the system changes. This change is equal to the force that Stephen exerts on David multiplied by the distance David moves.

2 The energy in the system changes. This change is equal to the force that Stephen exerts on David multiplied by the distance David moves multiplied by the cos 40o.

3 David is moving at a constant speed, thus the net force exerted on David is zero. Zero net force means zero work. Thus, the energy of the system does not change.

Kinitial + Ug initial + Us initial + W = Kfinal + Ug final + Us final +DEint

A situation is described with a bar chart and in words. Which verbal description matches this bar chart?

1 An object fell off a cliff and the energy in the system was transferred from gravitational potential energy to kinetic energy.

2 A spring on a table shot an object. Youmeasured the kinetic energy of the object when it landed at the same elevation.

3 A spring shot an object vertically from a height above the ground. You then measure the kinetic energy at ground level just before the ball hits the ground.

y

t, y = h

ti, yi = 0

v = constant

Earth

Ko + UgoWK + Ug + Us

1

2

3

A situation is represented pictorially below. Which bar chart best matches the picture?

= constant

x

Earth

Tim is carrying a basket of laundry to be washed. This motion is represented by a free body diagram and a motion diagram.

Which verbal description best matches the diagrams? (The earth and basket are the system)

• Since the basket is moving, work is done on the basket and that is all we are able to tell.

• Tim does work, but the systems energy does not change.

• The velocity is constant, the height is constant and Tim is doing work. The internal energy of the system must be increasing.

• No work is being done on the system which implies the system’s energy does not change.

Which energy bar chart best matches this situation as the car goes to the bottom?

hi=h

vi=0

Ki + UgiW = Kf + Ugf

h>hf >0

1

vf >0

Ki + UgiW = Kf + Ugf

Ki + UgiW = Kf + Ugf

3

2

If the same coaster was not frictionless, which bar chart would describe that process?

hi=h

vi=0

Ki + UgiW = Kf + Ugf + DE

h>hf >0

1

vf >0

3

Ki + UgiW = Kf + Ugf

Ki + UgiW = Kf + Ugf + DE

2

A roller coaster car’s trip is described by the energy bar chart shown below.

Ki + UgiW = Kf + Ugf

Which final point in the picture below matches the bar chart?

Initial

1 Final

3 Final

y

5 Final

2 Final

0

4 Final

The energy bar chart below represents a car’s motion. bar chart shown below.

Ki + UgiW = Kf + DE

Which motion diagram matches this situation?

2

1

4

3

A car is moving horizontally as described by the motion diagram below.

Which energy bar chart best matches this?

Ki + UgiW = Kf + Ugf

2

Ki + UgiW = Kf + Ugf

1

4

3

Ki + UgiW = Kf + Ugf

Ki + UgiW = Kf + Ugf

Tim is moving a basket of laundry and his hands exert a force on the basket equal in magnitude to the force of the Earth on the basket.

Which energy bar chart(s) could match this situation? (The earth and basket are the system)

Ki + UgiW = Kf + Ugf

Ki + UgiW = Kf + Ugf

1

2

Ki + UgiW = Kf + Ugf

Ki + UgiW = Kf + Ugf

4

3

5 3 & 4 6 2, 3 & 4