Question 1

A block of mass $$m$$ slides across a horizontal surface with kinetic friction. If the block is the system, is it considered an isolated or nonisolated system?

Accepted Answer

Nonisolated, because friction transfers energy out of the block.

Question 2

A ball of mass $$m is $$dropped from a height $$h$$ above the ground. Neglecting air resistance, what is the speed $$v of $$the ball when it is at a height $$y$$ above the ground?

Accepted Answer

$$v = \sqrt{2g(h-y)}$$

Question 3

Which of the following is NOT a valid mechanism for energy transfer across a system boundary?

Accepted Answer

Conservation of force

Question 4

A 6.0-kg block is pulled 3.0 m along a horizontal surface by a 12 N force. The coefficient of kinetic friction is 0.15. What is the speed of the block after moving 3.0 m? (Assume $$g = 9.8\ \mathrm{m/s^2$})$$

Accepted Answer

$$v = 3.2\ \mathrm{m/s}$$

Question 5

A block of mass $$1.6\ \mathrm{kg} is $$attached to a horizontal spring with force constant $$900\ \mathrm{N/m}$$, compressed $$2.0\ \mathrm{cm}$$ and released from rest. What is the speed of the block as it passes through equilibrium (frictionless surface)?

Accepted Answer

$$v = 1.06\ \mathrm{m/s}$$

Question 6

A rock of mass $$m is $$dropped from height $$A. A $$second rock, mass $$2m$$, is dropped from the same height. When the second rock strikes the ground, what is its kinetic energy compared to the first?

Accepted Answer

Twice that of the first rock

Question 7

Three identical balls are thrown from the top of a building with the same initial speed: one horizontally, one at an angle above, and one at an angle below the horizontal. Neglecting air resistance, how do their speeds compare as they hit the ground?

Accepted Answer

All have the same speed

Question 8

Which of the following best describes the energy transformation when a car suddenly skids to a stop on a freeway?

Accepted Answer

Some kinetic energy becomes internal energy, some is transferred away by mechanical waves

Question 9

Which equation correctly expresses the work-kinetic energy theorem for a nonisolated system?

Accepted Answer

$$W_{ext} = \Delta K$$

Question 10

A spring-loaded popgun launches a projectile of mass $$m to a $$height $$y_0$$ above the launch point. If the spring is compressed by $$x_0$$ and has a spring constant $$k$$, what is the equation for conservation of energy (neglecting resistive forces)?

Accepted Answer

$$\frac{1}{2}kx_0$^2 = $$mgy_0$$

Question 11

Which of the following is the correct formula for average power?

Accepted Answer

$$P_{avg} = \frac{W}{\Delta t}$$

Question 12

A refrigerator is rolled up a ramp into a truck. If the work done is the same for two different ramp lengths, but one takes twice as long, how does the power output compare?

Accepted Answer

The power is half as much for the longer time

Question 13

Which of the following is true for an isolated system?

Accepted Answer

Total energy is conserved

Question 14

A block is pulled across a rough surface. Which equation best describes the change in mechanical energy due to nonconservative forces?

Accepted Answer

$$\Delta E_{mech} = W_{nc}$$

Question 15

Which of the following is the SI unit for power?

Accepted Answer

Watt

Question 16

Energy leaves a lightbulb primarily by which mechanism?

Accepted Answer

Electromagnetic radiation

Question 17

If energy is transferred to a block by a hand pushing it, what type of energy transfer is this?

Accepted Answer

Mechanical work

Conservation of Energy and Its Applications

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