Chapter 4 Pretest

1. A body is NOT in equilibrium if: A) it is moving at constant speed in a straight line, B) there is an unbalanced force acting on the body, C) it is at rest, D) its motion is unchanged.

1. A body is NOT in equilibrium if: A) it is moving at constant speed in a straight line, B) there is an unbalanced force acting on the body, C) it is at rest, D) its motion is unchanged.

2. Resolution of forces is the procedure for finding: A) parallel forces, B) component forces, C) equilibrant forces, D) resultant forces.

2. Resolution of forces is the procedure for finding: A) parallel forces, B) component forces, C) equilibrant forces, D) resultant forces.

3. Friction is a disadvantage: A) in walking along a sidewalk, B) in automobile brakes, C) in roller bearings on freight cars, D) between bike tires and the dirt trail.

3. Friction is a disadvantage: A) in walking along a sidewalk, B) in automobile brakes, C) in roller bearings on freight cars, D) between bike tires and the dirt trail.

4. Which of the following statements about friction is FALSE 4. Which of the following statements about friction is FALSE? Friction: A) involves objects that are in physical contact, B) is less if surfaces are very smooth, C) is a force that resists motion, D) is caused by uneven surfaces of touching objects.

4. Which of the following statements about friction is FALSE 4. Which of the following statements about friction is FALSE? Friction: A) involves objects that are in physical contact, B) is less if surfaces are very smooth, C) is a force that resists motion, D) is caused by uneven surfaces of touching objects.

5. A box is pulled along a level floor at constant speed by a rope that makes a 45 degree angle with the floor. The box weighs 100 N. The coefficient of sliding friction is 0.75. The force exerted on the rope is: A) 75 N, B) between 75 N and 100 N, C) 100 N, D) greater than 100 N.

5. A box is pulled along a level floor at constant speed by a rope that makes a 45 degree angle with the floor. The box weighs 100 N. The coefficient of sliding friction is 0.75. The force exerted on the rope is: A) 75 N, B) between 75 N and 100 N, C) 100 N, D) greater than 100 N. The correct answer is 60.6 N. The writer of this question forgot to allow for the decrease of the normal force due to the upward component of the force on the rope. Even the eggheads make mistakes!

6. What causes a moving object to change direction. a. acceleration. b 6. What causes a moving object to change direction? a. acceleration b. velocity c. inertia d. force

6. What causes a moving object to change direction. a. acceleration. b 6. What causes a moving object to change direction? a. acceleration b. velocity c. inertia d. force

7. Which of the following is the tendency of an object to maintain its state of motion? a. acceleration b. inertia c. force d. velocity

7. Which of the following is the tendency of an object to maintain its state of motion? a. acceleration b. inertia c. force d. velocity

8. A wagon with a weight of 300.0 N is accelerated across a level surface at 0.5 m/s2. What net force acts on the wagon? a. 9.0 N b. 15 N c. 150 N d. 610 N

8. A wagon with a weight of 300.0 N is accelerated across a level surface at 0.5 m/s2. What net force acts on the wagon? a. 9.0 N b. 15 N c. 150 N d. 610 N

9. The statement by Newton that for every action there is an equal and opposite reaction is which of his laws of motion? a. first b. second c. third d. fourth

9. The statement by Newton that for every action there is an equal and opposite reaction is which of his laws of motion? a. first b. second c. third d. fourth

10. The magnitude of the force of gravity acting on an object is: a 10. The magnitude of the force of gravity acting on an object is: a. frictional force b. weight c. inertia d. mass

10. The magnitude of the force of gravity acting on an object is: a 10. The magnitude of the force of gravity acting on an object is: a. frictional force b. weight c. inertia d. mass

1. Define equilibrium. What conditions are required for equilibrium?

Equilibrium exists when the net force on an object is zero Equilibrium exists when the net force on an object is zero. There is no acceleration.

2. On point 0, a force of 25. 0 N acts eastward and a force of 10 2. On point 0, a force of 25.0 N acts eastward and a force of 10.0 N acts southward. Calculate the magnitude and direction of the resultant force.

252 + 102 = c2 c = 27 N tanq = 10/25 22° south of east

3. A carton weighing 250 N is resting on a ramp that makes an angle of 20.0° with the horizontal. What are the magnitudes of the components of the weight of the carton parallel to the ramp and perpendicular to it?

The parallel component FII is the opposite and the perpendicular component F^ is the adjacent. sin 20° = FII/250 N FII = 85.5 N cos 20° = F^/250 N F^ = 235 N

4. If a steel block weighing 4 4. If a steel block weighing 4.63 N can be pulled at a constant speed across a smooth steel plate by a force of 2.64 N, what is the coefficient of sliding friction of steel on steel?

m = Ffriction/Fnormal m = 2.64 N/4.63 N m = 0.570

5. When a car is moving, what happens to the velocity and acceleration of the car if the air resistance becomes equal to the force acting in the opposite direction?

The acceleration drops to zero, and the velocity becomes constant The acceleration drops to zero, and the velocity becomes constant. (This is the same principle as terminal velocity.)

6. In a game of tug-of-war, a rope is pulled to the left with a force of 75 N and to the right with a force of 102 N. What is the magnitude and direction of the net external force on the rope?

102 N – 75 N = 27 N to the right.