Q: A medical X-ray tube accelerates electrons to a velocity of $$108\ \mathrm{m/s}$$ and then slams them into a tungsten target. If the mass of an electron is $$9.11 \times 10$$^{-31}$$\ \mathrm{kg}$$, what is the kinetic energy of one electron just before impact?

$$5.32 \times 10$$^{-27}$$\ \mathrm{J}$$

Question 1

A tsunami travels across the ocean with a speed given by $$v = \sqrt{g h}$$, where $$g is $$the acceleration due to gravity and $$h is $$the depth of the ocean. If $$g = 9.80\ \mathrm{m/s^2$}$$ and $$h = 2994\ \mathrm{m}$$, what is the speed of the tsunami?

Accepted Answer

$$v = 171\ \mathrm{m/s}$$

Question 2

The average American uses electrical energy at the rate of about $$1.5\ \mathrm{kW}. If $$solar energy reaches Earth's surface at an average rate of $$1000\ \mathrm{W/m^2$}$$, what fraction of the United States' land area (about $$9.4 	imes 10^6$\ \mathrm{km^2$}) $$would have to be covered with $$20\%$$ efficient solar cells to provide all our electrical energy needs? Assume $$330,000,000$$ Americans.

Accepted Answer

About $$1.2\% of $$the land area

Question 3

A model rocket is launched straight upward. Its altitude $$y as a $$function of time is given by $$y = b t - c t^2$, where b = 80.0$$\ \mathrm{m/s}$$ and c = 4.91$$\ \mathrm{$$m/s^2$$}$$. At what time does the rocket reach its maximum altitude?

Accepted Answer

$$t = 16.3\ \mathrm{s}$$

Question 4

A medical X-ray tube accelerates electrons to a velocity of $$108\ \mathrm{m/s}$$ and then slams them into a tungsten target. If the mass of an electron is $$9.11 	imes 10$$^{-31}$$\ \mathrm{kg}$$, what is the kinetic energy of one electron just before impact?

Accepted Answer

$$5.32 	imes 10$$^{-27}$$\ \mathrm{J}$$

Question 5

A carpenter tosses a shingle horizontally off an $$8.8\ \mathrm{m}$$ high roof at $$11.0\ \mathrm{m/s}. $$How long does it take the shingle to reach the ground?

Accepted Answer

$$1.34\ \mathrm{s}$$

Question 6

Pilots of high-performance aircraft risk loss of consciousness if they undergo accelerations exceeding about $$5g. $$For a military jet flying at $$2470\ \mathrm{km/h}$$, what is the minimum radius for a turn that will keep the acceleration below $$5g$$?

Accepted Answer

$$r = 3.80\ \mathrm{km}$$

Question 7

Your spaceship lands on one of the Sun's planets. If your weight is $$528\ \mathrm{N} on $$Earth, what is your weight on Jupiter, where $$g = 24.5\ \mathrm{m/s^2$}$$?

Accepted Answer

$$1320\ \mathrm{N}$$

Question 8

A hockey player whacks a $$162\ \mathrm{g}$$ puck with a stick, applying a $$212\ \mathrm{N}$$ force that accelerates it to $$78.3\ \mathrm{m/s}. If $$the puck was initially at rest, for how much time did the acceleration last?

Accepted Answer

$$0.060\ \mathrm{s}$$

Question 9

Two forces act on a $$3.1\ \mathrm{kg}$$ mass that undergoes acceleration $$a = 0.91 - 0.27\ \mathrm{m/s^2$}. If $$one force is $$1.42 - 2.5\ \mathrm{N}$$, what is the other force?

Accepted Answer

$$1.38 - 2.63\ \mathrm{N}$$

Question 10

Movers slide a $$73\ \mathrm{kg}$$ file cabinet at constant speed in a straight line along a floor where the coefficient of kinetic friction is $$0.81. $$What is the frictional force on the cabinet?

Accepted Answer

$$580\ \mathrm{N}$$

Question 11

Find the work done by a force $$\vec{F} = 1.8\hat{i} + 2.2\hat{j}\ \mathrm{N} as it $$acts on an object moving from the origin to the point $$5.6\hat{i} + 3.3\hat{j}\ \mathrm{m}.$$

Accepted Answer

$$17.0\ \mathrm{J}$$

Question 12

A hospital patient’s leg slipped off a stretcher and hit the floor. The defense attorney claims the leg, with mass $$8\ \mathrm{kg}$$, hit the floor with a force equal to its weight ($$\approx 80\ \mathrm{N}). $$You argue the leg had dropped freely for $$0.27\ \mathrm{m}$$, then hit the floor and stopped in $$2\ \mathrm{cm}. $$What is the average force exerted on the heel during the impact?

Accepted Answer

$$4800\ \mathrm{N}$$

Question 13

Which of the following best describes the difference between static and kinetic friction?

Accepted Answer

Static friction prevents motion up to a maximum value, while kinetic friction acts during motion and is usually less than the maximum static friction.

Question 14

A ball is thrown straight up with an initial velocity of $$20\ \mathrm{m/s}. $$Neglecting air resistance, what is its velocity after $$2.0\ \mathrm{s}$$?

Accepted Answer

$$0.4\ \mathrm{m/s}$$

Question 15

A $$2.0\ \mathrm{kg}$$ block slides down a $$30^\circ$$ incline with a coefficient of kinetic friction $$\mu_k = 0.15. $$What is the acceleration of the block?

Accepted Answer

$$3.1\ \mathrm{m/s^2$}$$

Question 16

A $$5.0\ \mathrm{kg}$$ object is acted on by a $$20\ \mathrm{N}$$ force at an angle of $$30^\circ$$ above the horizontal. What is the horizontal acceleration of the object?

Accepted Answer

$$3.46\ \mathrm{m/s^2$}$$

Question 17

A $$0.50\ \mathrm{kg}$$ ball is dropped from a height of $$2.0\ \mathrm{m}. $$What is its speed just before it hits the ground?

Accepted Answer

$$6.3\ \mathrm{m/s}$$

Question 18

A $$1.0\ \mathrm{kg}$$ object moves in a circle of radius $$2.0\ \mathrm{m} at a $$constant speed of $$3.0\ \mathrm{m/s}. $$What is the magnitude of the centripetal force?

Accepted Answer

$$4.5\ \mathrm{N}$$

Physics Exam Study Guide: Chapters 1–6 (Mechanics, Forces, and Energy)

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