Unit B Energy Flow in Technological Systems

Unit B—Energy Flow in Technological Systems

Unit Assessment

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Section B2.0 Quiz
(20 Marks)

1. For each technology listed in the table below, fill in the answers to the following questions:

a) What is the main type of energy conversion evident?

b) Name the scientist chiefly responsible for its discovery.

c) Identify a specific area in science, technology, or society where the device or technology could be used.

Technology / Main Energy Conversion / Discoverer / Where It Could Be Used
an electromagnet
a generator
an electric light
a thermocouple

2. Scientists of the early 1600s could not explain the experiment that used Newton’s cradle.

a) Draw a diagram of the demonstration apparatus in the space below.

b) Briefly describe what happens in the demonstration.

Unit B—Energy Flow in Technological Systems

c) Explain why the ball on the opposite side rises to the same height. Use the theory believed in the 1600s and compare it with the theory of today.

3. In the space below, draw a labelled diagram of the apparatus that Joule used to prove a connection between potential energy and heat. Describe how the experiment works.

4. a) What is the weight of a 45.0-kg object?

b) What are three differences between the mass of an object and the weight of the same object?

5. A 40.0-kg student climbs up a ladder to the roof of a building. The gravitational potential energy of the student at this point is 2.00 x 103 J. How high is the student above the ground?

Unit B—Energy Flow in Technological Systems

6. A force of 50.0 N is used to stretch an elastic so that it has 40.0 J of elastic potential energy. Through what distance was the elastic stretched?

7. A curling rock with a mass of 20.0 kg slides down a sheet of ice at a speed of
6.00 m/s. What is the kinetic energy of the curling rock?

8. A 200-g Nerf dart is shot from a dart gun with a kinetic energy of 3.60 J. What was the initial speed of the dart?

9. An elastic band is stretched a distance of 15.0 cm by a force of 10.0 N.

a) How much work was done in stretching the elastic?

b) How much elastic potential energy is stored in the elastic?

c) What assumption did you make in answering question (b)?

d) A 1.00-g object is placed on the elastic, and the elastic is released in a vertical direction. How much kinetic energy is transferred to the object by the elastic?

e) What was the speed of the object at the point that it leaves the elastic?

Unit B—Energy Flow in Technological Systems

f) What assumption did you make in answering question (e)?

g) How high will the object in question (d) rise?

h) What assumption did you make in answering question (g)?

10. A 50.0-kg student climbs a flight of stairs a vertical distance of 3.00 m. What is the gravitational potential energy stored in the student?

11. What principal type of energy conversion takes place in a solar cell? Why are solar cells ideal for use as energy sources in space?

12. How are a battery and a hydrogen fuel cell alike?

Unit B—Energy Flow in Technological Systems

Answers to Section B2.0 Quiz

Technology / Main Energy Conversion / Discoverer / Where It Could Be Used
[Answers will vary but could include the following]
an electromagnet / electric to magnetic / Oersted / lifting magnets in industry or sucking coils in appliances
a generator / magnetic to electric / Faraday / electrical generators
an electric light / electric to light / Edison / light bulbs
a thermocouple / heat to mechanical / Seebeck / thermostats

2. a) The diagram should resemble Fig. B2.6 on page 167 of the student book.

b) In the Newton’s cradle experiment, a ball is lifted to a height and released. It collides with other balls in a row, and a ball at the other end rises to the same height as the original ball.

c) 1600s—This was explained by saying that a living force, vis viva, was being transmitted through the balls from the motion of the first ball. This force caused the other ball to rise to the same height.

Present—The first ball is given potential energy when it is lifted away. As the ball returns to its starting position, it is converting potential energy to kinetic energy. In the collision, this energy is transmitted to the balls in the row, and the ball on the other side. The ball on the other side rises to the same height to give it the same amount of potential energy as the first ball.

3. Explanation: A hanging block of wood attached to a string has potential energy. When released, the block falls, turning a shaft with attached blades. As the blades rotate with mechanical energy, the mechanical energy is transformed into heat, thus heating up the water.

4. a) 441 N

b) Mass is scalar; weight is a vector.

Mass is measured in kilograms; weight is measured in newtons.

Mass is constant; weight varies with the value of “g” (acceleration due to gravity).

Mass is defined as the inertia of an object; weight is defined as the gravitational force acting on a mass.

5. 5.10 m

6. 0.800 m

7. 360 J

8. 6.00 m/s

9. a) 1.50 J

b) 1.50 J

c) work done = energy gain; no energy is lost to other forms of energy

Unit B—Energy Flow in Technological Systems

d) Ep = Ek = 1.50 J

e) 54.8 m/s

f) Assumed that all the potential energy is converted to kinetic energy

g) 153 m

h) Assumed that all the kinetic energy was converted to potential energy

10. 1.47 ´ 103 J

11. Solar energy is converted into electricity similar to a battery. However, the solar cell does not operate from a chemical reaction like a battery so it never needs recharging or maintenance.

12. A battery and a hydrogen fuel cell both produce electricity.