## Homework Helpers: Physics

## 2 Forces and the Laws of Motion

### Chapter 2 Examination

**Part I—Matching**

Match the following terms to the definitions that follow.

a. force

b. net force

c. friction

d. contact force

e. weight

f. static friction

g. field force

h. inertia

i. kinetic friction

_______1.__ A force that exists between two objects that are touching, which resists their motion relative to each other.

_______2.__ The force of attraction between two objects due to gravity.

_______3.__ The sum of all of the forces acting on an object.

_______4.__ An object”s tendency to resist changes in motion.

**Part II—Multiple Choice**

For each of the following questions, select the best answer.

__5.__ How much force is required to cause a ball with a weight of 3.00 N to accelerate at a rate of 3 m/s?

a) 1 N b) 3 N c) 9 N d) 12 N

__6.__ Forces of 6.0 N and 9.0 N act at right angles to each other on the same box. What is the magnitude of the resultant of these two forces?

a) 15 N b) 3.0 N c) 11 N d) 1.5 N

__7.__ A box with a mass of 22.5 kg experiences an acceleration of 4.50 m/s^{2}. Find the net force acting on the object.

a) 101 N b) 5.00 N c) 18.0 N d) 27.0 N

__8.__ A block of wood with a weight of 5.0 N sits on a horizontal surface. A girl finds that she must apply a force of 2.0 N to overcome the force of friction and get the block to start sliding. What is the coefficient of static friction between the surfaces?

a) 7.0 b) 3.0 c) 0.40 d) 2.5

__9.__ An ice skater is at rest on the surface of the ice. Compared to the force the skater exerts on the ice, the force that the ice exerts on the skater is

a) greater

b) less

c) the same

d) not enough information given

__10.__ A girl tries to get her dog to start walking by applying a gentle force of 2.8 N to his leash at an angle of 60.0° above the horizontal. What is the magnitude of the horizontal component (F_{x}) of this applied force?

a) 1.2 N b) 1.4 N c) 1.8 N d) 2.0 N

__11.__ A desk with a weight 670 N rests on a floor where the coefficient of static friction between the surfaces is 0.45. How much force would be required to get the desk to start sliding?

a) 3.0 × 10^{2} N

b) 1.5 × 10^{2} N

c) 3.1 × 10^{1} N

d) 3.3 × 10^{3} N

__12.__ A resultant force of 11.0 N is made up of two component forces acting at right angles to each other. If the magnitude of one of the component forces is 6.00 N, what is the magnitude of the other force?

a) 7.00 N b) 9.22 N c) 11.7 N d) 15.0 N

__13.__ Two students want to work together to push a heavy lab table across the floor. The resultant force will be greatest if the angle between their component forces is:

a) 0° b) 45° c) 90° d) 180°

__14.__ Two forces with magnitudes of 5.0 N and 16.0 N act on the same object at an angle of 180° to each other. What is the magnitude of the resultant force?

a) 11.0 N b) 15 N c) 17.0 N d) 21 N

**Part III—Calculations**

Perform the following calculations.

__15.__ A girl pushes a 10.0 N book across a table with a horizontal applied force of 15.0 N. If the coefficient of friction between the book and table is 0.35, find its acceleration.

__16.__ A 5.00 kg wood block slides with uniform velocity down an inclined plane at an angle of 33.0° above the horizontal. Find the coefficient of kinetic friction between the block and the inclined plane.

__17.__ A box with a mass of 22.0 kg is placed on a ramp that is at an angle of 38.0° above the horizontal. What is the magnitude of the component of the weight that is parallel to the surface of the ramp?

__18.__ A woman applies a horizontal force of 50.0 N to push a 200.0 N across the floor. If the force of friction between the floor and the couch is 20.0 N, what will be the acceleration of the couch?

__19.__ A man with a weight of 868 N stands on a scale in an elevator that is accelerating upwards at a rate of 2.50 m/s^{2}. Assuming the scale measures weight in newtons, what will the scale read?

__20.__ The same man from problem 19 is still standing on the scale in the elevator when it starts to accelerate downwards at a rate of 3.80 m/s^{2}. What will the scale read at this time?