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Exam: 286039RR – Engineering Mechanics, Part 4

1. The characteristics of a force are indicated in Examination Figure 3. If this force acts on a certain body for 4 sec, the magnitude of the vertical component of the linear impulse of the force during that interval of time would be

A. 276 lb-sec.

B. 240 lb-sec.

C. 138 lb-sec.

D. 190 lb-sec.

2. The radius of a cylindrical flywheel is 2 ft and the weight of the flywheel is 350 lb. A force whose constant magnitude is 40 lb is applied to the rim of the wheel along a line that is tangent to the rim. The magnitude of the angular acceleration of the wheel would be

A. 3.69 rad per sec per sec.

B. 2.90 rad per sec per sec.

C. 1.84 rad per sec per sec.

D. 2.25 rad per sec per sec.

3. The diameter of a solid wheel is 3.5 ft, and its weight is 60 lb. The wheel is rolled toward the left along a horizontal surface under the action of a horizontal force whose magnitude is 20 lb. If the friction force is sufficient to prevent slipping, what is the magnitude of the linear acceleration of the center of gravity of the wheel?

A. 3.21 fps per sec

B. 8.15 fps per sec

C. 5.32 fps per sec

D. 7.16 fps per sec

4. As indicated in Examination Figure 1, a steel ball which weighs 800 lb is suspended from a long cable so that it can swing in a vertical plane. When the cable was vertical during a certain swing, the magnitude of the linear velocity of the ball was 18 fps. The kinetic energy of translation of the ball at that instant was

A. 14,400 ft-lb.

B. 445 ft-lb.

C. 8040 ft-lb.

D. 4025 ft-lb.

5. A solid sphere whose diameter is 3.5 ft weighs 600 lb. The mass moment of inertia of the sphere with respect to a horizontal line through its center of gravity is

A. 45.6 slug-ft

B. 28.5 slug-ft

C. 36.0 slug-ft

D. 22.8 slug-ft

6. A truck with a velocity of 35 mph is traveling along a horizontal stretch of highway. If the total weight of the truck and its contents is 8400 lb, the magnitude of the linear momentum of the truck is

A. 9150 lb-sec.

B. 18,300 lb-sec.

C. 11,250 lb-sec.

D. 13,390 lb-sec.

7. An automobile weighing 3220 lb and having a uniform linear velocity of 55 mph was traveling along a curved portion of a highway. If the radius of the curve was 600 ft, the magnitude of the centrifugal force was

A. 650 lb.

B. 1085 lb.

C. 872 lb.

D. 503 lb.

8. A body that is under the action of a system of forces moves along a straight path. One force of the system has a constant magnitude equal to 200 lb, and the angle between the line of action of this force and the path of the moving body is 20º. If the body moved 3 ft along its path during 5 sec, how much work was done on the body by the specified force during that time interval?

A. 269 ft-lb

B. 564 ft-lb

C. 435 ft-lb

D. 329 ft-lb

9. An elevator car in a building is expected to move upward with an acceleration whose magnitude is 6 fps per sec when the magnitude of the force that tends to lift the car is 4000 lb. If the effect of friction is neglected, the greatest total weight of the car and its contents can be

A. 3160 lb.

B. 3000 lb.

C. 3290 lb.

D. 3370 lb.

10. When a body is rotating under the action of a system of forces and the resultant moment of all forces does not change, the body is subjected to a/an

A. uniform angular acceleration.

B. mass moment of inertia.

C. centripetal force.

D. axis of rotation.

11. Blocks 1 and ,2 in Examination Figure 6 are connected by a cable, which passes over a sheave. Block 1 slides along a horizontal surface under the action of a horizontal force applied by the cable when block 2 is permitted to fall vertically through the air. Block 1 weighs 120 lb, block 2 weighs 50 lb, the coefficient of friction for the materials of block 1 and the supporting surface is 0.3, and friction in the sheave can be neglected. At the instant at which the blocks were in the positions shown, the magnitude of the velocity of each block was 5 fps. After block 2 has moved 3 ft downward from the position shown, the magnitude of the velocity of each block would be

A. 7.30 fps.

B. 6.40 fps.

C. 6.75 fps.

D. 7.04 fps.

12. The diameter of the right circular cylinder represented in front elevation in Examination Figure 2 is 9 in., the length of the cylinder is 8 ft, and the weight of the cylinder is 150 lb. The specified reference line for the mass moment of inertia of the cylinder is a vertical line perpendicular to the axis of the cylinder and passing through the centroid of a cross section of the cylinder. The section is located 1 ft from the righthand

end of the cylinder. The required mass moment of inertia is

A. 25.0 slug-ft

B. 66.9 slug-ft

C. 41.9 slug-ft

D. 83.8 slug-ft

13. As indicated in Examination Figure 4 on the next page, one end of a spring is attached to a stationary

fixture and the other end of the spring is attached to a block that can only move on a horizontal supporting

surface along a certain straight line. The natural length of the spring is 8 in., and the constant for it is 10 lb

per in. When the spring is vertical, as indicated in the illustration, its actual length is 9

1

in. If the block is

moved toward the left for a horizontal distance equal to 15 in., the amount of work required to deform the

spring during this movement of the block is

A. 232 in-lb.

B. 465 in-lb.

C. 830 in-lb.

D. 83 in-lb.

14. A spring has a normal length equal to 15 in. and the constant for it is 4 lb per in. One end of the spring is attached to a stationary support, and the other end of the spring is attached to a movable block which can only travel along a straight horizontal path. After the block has been moved so that the length of the spring was reduced to 10 in., the force that was applied to the block to cause this movement was taken away and the spring was permitted to return to its original length. The amount of work done by the spring in bringing the block back to its original starting position was

A. 50 in-lb.

B. 125 in-lb.

C. 250 in-lb.

D. 175 in-lb.

15. The force that acts toward the center of the circle along a radial line is known as

A. liner acceleration.

B. centripetal force.

C. linear velocity.

D. centrifugal force.

16. The usual equation of motion for translation along a straight path is

A. F= ma.

B. Fx= ma.

C. A=mz.

D. △t = F.

17. The normal length of a spring is 6 in., and the spring constant is 20 lb per inch. How much work would have to be done on the spring to reduce its length from 6 in. to 4.5 in.?

A. 22.5 in.-lb

B. 32.5 in.-lb

C. 80 in.-lb

D. 12.2 in.-lb

18. A solid wheel is being rolled toward the right along a horizontal surface by a force whose line of action is horizontal. The diameter of the wheel is 2.5 ft, the wheel weighs 80 lb, and the magnitude of the force is 15 lb. If the friction force is sufficient to prevent slipping of the wheel on the supporting surface, the magnitude of the linear acceleration of the center of gravity would be

A. 4.03 fps per sec.

B. 3.22 fps per sec.

C. 5.15 fps per sec.

D. 6.44 fps per sec.

19. An automobile weighing 3600 lb and having a uniform linear velocity of 50 mph was traveling along a curved portion of highway. If the radius of the curve was 720 ft, the magnitude of the centrifugal force was

A. 872 lb.

B. 503 lb.

C. 835 lb.

D. 650 lb.

20. As indicated in Examination Figure 5, a solid cylindrical disk is caused to rotate about a stationary axis, which passes through the center of gravity of the disk. The force that produces rotation is applied to the rim of the disk by means of a cable, which is wound around the disk and is attached to a body. The radius of the disk is 2.5 ft, the weight of the disk is 800 lb, and the weight of the body is 300 lb. When the body is

supported in the position shown, the body and the disk are at rest. If the support tor the body is taken away, the disk will rotate without friction while the body moves downward under the action of its weight.

The angular velocity of the disk after the body has moved 5 ft from the position shown would be

A. 6.70 rad per sec.

B. 5.70 rad per sec.

C. 3.70 rad per sec.

D. 4.70 rad per sec.