# Kinematics and Forces of Objects

1) A 2-kg ball is moving with a constant speed of 5 m/s in a horizontal circle whose radius is 50 cm. What is the magnitude of the net force on the ball?

a. 0 N

b. 20 N

c. 40 N

d. 100 N

2) Kepler's second law tells us that planets sweep out equal areas in equal times. If you compare the amount of area per time swept by Earth with the one of Jupiter, you would conclude:

a. They sweep the same area per time.

b. They sweep different areas per time.

c. Jupiter sweeps a larger area per time because it has much more mass than Earth.

d. Earth sweeps a larger area per time because it has much less mass than Jupiter.

3) A sewing machine needle moves up and down in simple harmonic motion with an amplitude of 1.27 cm and a frequency of 2.55 Hz. What is the maximum acceleration of the needle?

a. 8.26 cm/s2

b. 16.5 cm/s2

c. 326 cm/s2

d. 163 cm/s2

4) A flatbed truck is carrying a 20.0-kg crate along a level road. The coefficient of static friction between the crate and the bed is 0.400. What is the maximum acceleration that the truck can have if the crate is to stay in place?

a. 3.92 m/s squared.

b. 8.00 m/s squared.

c. 78.5 m/s squared.

d. 196 m/s squared.

5) A student adds two perpendicular displacement vectors of magnitude 12.0 cm and 8.0 cm. Which of the following is the only choice for the magnitude of the resultant displacement of these two vectors?

a. 8.9 cm

b. 4.0 cm

c. 20.0 cm

d. 14.4 cm

6) An object is moving in a circular path with an angular speed of 1.52 rad/s. How long does it take the object to complete one revolution?

a. 4.13 s

b. 2.07 s

c. 118 s

d. 4.77 s

7) A man is holding an 8.00-kg vacuum cleaner at arm's length, a distance of 0.550 m from his shoulder. What is the torque on the shoulder joint if the arm is horizontal?

a. 4.40 Nm

b. 43.2 Nm

c. 14.5 Nm

d. 0 Nm

8) When a parachutist jumps from an airplane, he eventually reaches a constant speed, called the terminal velocity. This means that:

a. The acceleration is equal to g.

b. The force of air resistance is equal to zero N.

c. The effect of gravity has died down.

d. The force of air resistance is equal to the weight of the parachutist.

9) What should the height of a slide in a park be so that a child will reach the bottom of the slide with a speed of 15.0 m/s? Use g = 10.0 m/s squared.

a. 22.5 m

b. 15.1 m

c. 11.3 m

d. 10.5 m

10) A 1959 penny has a diameter of 19.55 mm, a thickness of 1.55 mm, and a mass of 2.500 g. What is its density?

a. 5.37 x 10 to power of (3) kg/m cubed.

b. 21.5 x 10 to power of (3) kg/m cubed.

c. 1.34 x 10 to power of (3) kg/m cubed.

d. 2.68 x 10 to power of (3) kg/m cubed.

11) By what amount does the intensity level decrease when you triple your distance from a source of sound?

a. 9.5 dB

b. 4.8 dB

c. 6.0 dB

d. 3.0 dB

12) A stone is thrown straight up. When it reaches its highest point:

a. Its velocity is zero m/s.

b. Its acceleration is zero m/s.

c. Both its velocity and acceleration are zero m/s.

d. Neither is zero m/s.

13) The ratio of the final kinetic energy to the initial kinetic energy of an object is one half. If the initial velocity of the object is 10 m/s, what is the final velocity?

a. 20 m/s

b. 20 m/s squared

c. 7.1 m/s

d. 7.1 m/s squared

14) The deepest point of the Pacific Ocean is 11,033 m, in the Mariana Trench. What is the water pressure at that point? The density of seawater is 1025 kg/m cubed.

a. 5.55 x 10 to power of (7) Pa

b. 8.88 x 10 to power of (7) Pa

c. 1.11 x 10 to power of (8) Pa

d. 2.22 x 10 to power of (8) Pa

15) A 2.0-m rope is lying on a table. You pick up one end and start raising it. How high above the table is the center of mass of the rope when half of the rope has lifted off the table?

a. 0.25 m

b. 0.50 m

c. 0.75 m

d. 1.0 m

16) During the time that the acceleration of a particle is constant, its velocity-vs-time curve is:

a. A straight line.

b. A parabola opening downward.

c. A parabola opening upward.

d. A curve other than a parabola.

17)Two boxes, one more massive than the other, rest in contact with one another on a smooth, level floor. A horizontal force F pushes on one or the other of the boxes. The contact force between the boxes:

a. Is larger when F is applied to the more massive box.

b. Is larger when F is applied to the less massive box.

c. Is equal in both cases.

d. Can be larger or smaller depending on the actual masses.

18) Marcia uses a bow to shoot an arrow with initial velocity of magnitude vO and at an angle theta above the horizontal. When the arrow returns to the same height from which it started:

a. The speed of the arrow is twice vO.

b. The speed of the arrow is 9.8 times larger than vO.

c. The speed of the arrow is again vO.

d. The speed of the arrow is the square root of (2 vO).

19) How much work is required to stretch a spring 25.2 cm if its force constant is 12.3 N/m?

a. 0.391 J

b. 3.10 J

c. 1.05 J

d. 0.381 J

20) The quartz crystal in a digital watch has a frequency of 32.8 kHz. What is its period of oscillation?

a. 3.05 x 10 to power of (-5) s

b. 9.58 x 10 to power of (-5) s

c. 1.91 x 10 to power of (-4) s

d. 9.71 x 10 to power of (-6) s

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#### Solution Summary

The solution answers 20 Multiple Choice Questions.

Problems on kinematics and dynamics

6.) An airplane flies due south with respect to the ground at an air speed of 900 km/h for 2.0 hr before turning and moving southwest with respect to the ground for 3.0 hr. During the entire trip, a wind blows in the easterly direction at 120 km/h. (a) What is the plane's average speed with respect to the ground? (b) What is the plane's average velocity with respect to the ground? (c) What is the final position vector?

7.) Five forces, all of the same magnitude F, act on an object of mass m at the origin of the coordinate system. Two of the forces are aligned along the x-axis; one is oriented in the +x direction and one in the -x direction. Two other forces are similarly aligned with the z-axis. The fifth force points int he +y direction. What are the direction and magnitude of the acceleraation of the object? If we had specified the forces in a different order, would the answer have been different?

8.) A father pulls his identical twins on identical sleds tied one after the other. He exerts a force F that makes an angle of 30 degrees with the horizontal and that leads to an acceleration of the two sleds. What is the tension in the rope that he is pulling? What is the tension in the rope that connects the front sled to the rear sled? The mass of each sled plus its twin is m. Assume that there is no friction between the sleds runners and the snow surface.

9.) A force of magnitude 8.0 N pushes on a horizontally stacked set of blocks on a frictionless surface with masses m1 = 2.0 kg, m2 = 3.0 kg, m3 = 4.0 kg. (a) What is the acceleration of the stack? (b) What are the forces on block 1 as well as the net force on this block? (c) Repeat part b for block 2. (d) Repeat part b for block 3.

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