Self-Test: Equilibrium Test #2
Suggested Time: 65 minutes

1. State the condition for rotational equilibrium.

 A. SF = 0 B. SF ¹ 0 C. St = 0 D. St ¹ 0

2.

A body is in static equilibrium when

 A. St = 0 only. B. SF = 0 only. C. SF = 0 and St = 0. D. SF = 0 and St ¹ 0.

3.

A 4.2 m long uniform post is supported by a cable having a tension of 1 700 N. What is the mass of this post?

 A. 160 kg B. 260 kg C. 300 kg D. 530 kg

4. An 85 kg object is suspended from a ceiling and attached to a wall.

What is the tension in the left-hand rope?

 A. 280 N B. 350 N C. 500 N D. 1100 N

5. A force F is applied to a uniform horizontal beam as shown in the diagram below.

Which of the following is a correct expression for the torque on the beam about pivot point P due to this force?

 A. F sinq × d B. F sinq × d / l C. F cosq × d D. F cosq × d / l

6.

A uniform 1.5 kg beam hinged at one end supports a 0.50 kg block. The beam is held level by a vertical 0.80 kg rod resting on a Newton scale at the other end.

What is the reading on the scale?

 A. 8.6 N B. 9.1 N C. 16 N D. 27 N

7. A student stands on a uniform 25 kg beam. The scale on the right end reads 350 N.

What is the mass of the student?

 A. 45 kg B. 54 kg C. 58 kg D. 89 kg

8.

A beam is to be kept horizontal by a cord. In which of the four situations shown below will the tension in the cord be least?

 A. B.
 C. D.
9. A uniform 0.122 kg rod of 0.90 m length is used to suspend two masses as shown below.

At what distance x should the 0.20 kg mass be placed to achieve static equilibrium?

 A. 0.30 m B. 0.50 m C. 0.63 m D. 0.75 m

10. A 7.8 kg restaurant sign is suspended as shown.

What are the magnitude and direction of the vertical force acting on the sign at point P?

 MAGNITUDE OF THE VERTICAL FORCE DIRECTION OF THE VERTICAL FORCE A. 25 N up B. 25 N down C. 51 N up D. 51 N down

11. A 15 kg uniform beam 2.40 m long is suspended from a wall and a ceiling as shown.

What is the tension in the supporting wire?

 A. 670 N B. 740 N C. 870 N D. 960 N

12.

The diagram shows the forces acting on a massless ladder resting on the floor and a frictionless slope.

As a person walks up the stationary ladder, what happens to the magnitude of the forces FN1and FN2?

 MAGNITUDE OF FN1 MAGNITUDE OF FN2 A. Decreases Decreases B. Decreases Increases C. Increases Decreases D. Increases Increases
13. A uniform 3.0 kg shelf of width 0.50 m is supported by a bracket, as shown in the diagram below.

What force does the bracket exert on the shelf?

 A. 7.4 N B. 38 N C. 48 N D. 57 N

14.

A circus performer on a unicycle of total mass 55 kg rides across a uniform 30 kg beam. The supports are placed equal distances from the ends of the beam.

a) When he is at the position shown, determine the forces exerted by the supports on the beam. (5 marks)

b) As the performer moves toward the right the force exerted by support B will

(Check one response.) (1 mark)

c) Using principles of physics, explain your answer to b). (3 marks)

15. A uniform 4.8 m long ladder of mass 16 kg leans against a frictionless vertical wall as shown in the diagram below.

If the coefficient of friction would between the ladder and floor is 0.30, could a 75 kg person climb all the way up the ladder? If not, how far up could the person climb? (7 marks)

16.

An object of mass, m, is suspended by two cords connected to a wall and to a 5.0 kg block resting on a table as shown.

A coefficient of friction of 0.47 exists between the 5.0 kg block and the table. What is the maximum mass, m, that can be hung from the cords before the 5.0 kg block begins to move? (7 marks)

17.

A 75 kg painter stands on a uniform 5.0 m board of mass 16 kg supported horizontally by two ladders. Find the forces exerted by each ladder on the board. (7 marks)

18.

A uniform 6.0 m-long boom has a mass of 55 kg. It is kept in position by a restraining cable attached three-quarters of the way along the boom.

What is the tension in this cable when the boom supports a 150 kg mass as shown? (7 marks)

19.

A uniform 12 kg beam of length 3.00 m holding a 45 kg mass is attached by a wire to a wall as shown.

What is the reaction force (magnitude and direction) at the pin? (7 marks)

20.

A 6.0 m uniform beam of mass 32 kg is suspended horizontally by a hinged end and a cable. A 93 kg object is connected to one end of the beam.

What is the magnitude of the horizontal force Fh that the hinge exerts on the beam? (7 marks)