Chapter 4 Study Guide with MC & Practice Problems

Short Answer Review Questions
Answer only the specific question asked.  It is not necessary to repeat the question in your answer.  However, all answers are expected to be complete.  Use a separate piece of paper as necessary.

	1.	Briefly describe how applying the brakes to stop a bicycle is an example of force.

	2.	What is the abbreviation of the unit newton?

	3.	Why is force not a scalar quantity?

	4.	Construct a free-body diagram of a car being towed.

	5.	In a free-body diagram of an object, why are forces exerted by the object not included in the diagram?

	6.	What is the natural tendency of an object that is in motion?

	7.	If two teams playing tug-of-war pull on a rope with equal but opposite forces, what is the net external force on the rope?

	8.	Describe the forces acting on a car as it moves along a level highway in still air at a constant speed.

	9.	For an object to be in equilibrium, the net force acting on the object must have what value?

	10.	Why does it require much less force to accelerate a low-mass object than it does to accelerate a high-mass object the same amount?

	11.	In the equation form of Newton’s second law, SF = ma, what does SF represent?

	12.	A block of wood supported by two concrete blocks is chopped in half by a karate instructor. Identify an action-reaction pair, and compare the forces exerted by each object.

	13.	Do action-reaction pairs result in equilibrium? Explain.

	14.	When a horse pulls on a cart, the cart pulls on the horse with an equal but opposite force. How is the horse able to pull the cart?

	15.	Distinguish between mass and weight.

	16.	How do mass and weight vary with altitude?

	17.	What happens to air resistance when an object accelerates?

	18.	In this text, what does the symbol m represent?

	19.	How does the coefficient of static friction for two surfaces in contact compare to the coefficient of kinetic friction for the same two surfaces?

Problems
Answer on a separate piece of paper or in a notebook for problems.  Show work, including a sketch, for complete credit.  Consult your syllabus for rubric and penalty details.  Problems marked (H) are for honors students.

	20.	A sled is pulled at a constant velocity across a horizontal snow surface. If a force of 8.0 ´ 10 N is being applied to the sled rope at an angle of 53° to the ground, what is the magnitude of the force of friction of the snow acting on the sled?

	21.	A wagon having a mass of 32 kg is accelerated across a level road at 0.50 m/s. What net force acts on the wagon horizontally?

	22.	A farmhand attaches a 25 kg bale of hay to one end of a rope passing over a frictionless pulley connected to a beam in the hay barn. Another farmhand then pulls down on the opposite end of the rope with a force of 277 N. Ignoring the mass of the rope, what will be the magnitude and direction of the bale’s acceleration if the gravitational force acting on it is 245 N?

	23.	An elevator weighing  N is supported by a steel cable. What is the tension in the cable when the elevator is accelerated upward at a rate of 3.00 m/s? (g = 9.81 m/s)

	24.	A sailboat with a mass of  kg experiences a tidal force of  N directed to the east and a wind force against its sails with a magnitude of  N directed toward the northwest (45.0° N of W). What is the magnitude of the resultant acceleration of the boat?  Solve graphically; (H) solve algebraically as well.

	25.	Basking in the sun, a 1.10 kg lizard lies on a flat rock tilted at an angle of 15.0° with respect to the horizontal. What is the magnitude of the normal force exerted by the rock on the lizard?

	26.	(H) A couch with a mass of 1.00 ´ 10 kg is placed on an adjustable ramp connected to a truck. As one end of the ramp is raised, the couch begins to move downward. If the couch slides down the ramp with an acceleration of 0.70 m/s when the ramp angle is 25.0°, what is the coefficient of kinetic friction between the ramp and the couch? (g = 9.81 m/s)

Explanation
Give as detailed an explanation as you can.  You are encouraged to use diagrams and algebraic relationships to support your explanation.

	27.	A 0.2 kg squirrel can misstep, fall from the top of a tall tree right to the ground, and scurry away, seemingly unhurt by the experience.  A 100 kg human would not be able to pull off such a feat without a parachute.  Explain 
(H) Assume that the shape, density and coefficient of drag of the falling squirrel are the same as that of the falling human.  Estimate the squirrel’s terminal velocity given that the human’s is approximately 70 mph.

Multiple Choice
Identify the letter of the choice that best completes the statement or answers the question.

____	28.	Which of the following is the cause of an acceleration?
a.	speed	b.	inertia	c.	force	d.	velocity	

____	29.	What causes a moving object to change direction?
a.	acceleration	b.	velocity	c.	inertia	d.	force	

____	30.	Which of the following forces arises from direct physical contact between two objects?
a.	gravitational force	c.	contact force	
b.	fundamental force	d.	field force	

____	31.	The length of a force vector represents the
a.	cause of the force.	c.	magnitude of the force.	
b.	direction of the force.	d.	type of force.	

____	32.	A free-body diagram represents all of the following except
a.	the object.	c.	forces exerted by the object.	
b.	forces as vectors.	d.	forces exerted on the object.	

____	33.	The free-body diagram shown above represents a car being pulled by a towing cable. In the diagram, which of the following is the gravitational force acting on the car?
a.	5800 N	b.	775 N	c.	14 700 N	d.	13 690 N	

____	34.	The free-body diagram shown above represents a car being pulled by a towing cable. In the diagram, the 5800 N force is
a.	the gravitational force acting on the car.	
b.	the backward force the road exerts on the car.	
c.	the upward force the road exerts on the car.	
d.	the force exerted by the towing cable on the car.	

____	35.	Which of the following is the tendency of an object to maintain its state of motion?
a.	acceleration	b.	inertia	c.	force	d.	velocity	

____	36.	A waitperson carrying a tray with a platter on it tips the tray at an angle of 12° below the horizontal. If the gravitational force on the platter is 5.0 N, what is the magnitude of the force parallel to the tray that tends to cause the platter to slide down the tray? (Disregard friction.)
a.	0.42 N	b.	1.0 N	c.	4.9 N	d.	5.0 N	

____	37.	A single force acts on an object. The components of this force act along the +x-axis and the –y-axis. The single force that will bring the object into equilibrium has components that act along the
a.	+x-axis and +y-axis.	c.	-x-axis and +y-axis.	
b.	+x-axis and -y-axis.	d.	-x-axis and -y-axis.	

____	38.	If a nonzero net force is acting on an object, then the object is definitely
a.	at rest.	c.	being accelerated.	
b.	moving with a constant velocity.	d.	losing mass.	

____	39.	In general, Fnet equals
a.	Ff.	b.	Fg.	c.	Fn.	d.	SF.	

____	40.	Two perpendicular forces, one of 45.0 N directed upward and the other of 60.0 N directed to the right, act simultaneously on an object with a mass of 35.0 kg. What is the magnitude of the resultant acceleration of the object?
a.	2.14 m/s	b.	3.00 m/s	c.	5.25 m/s	d.	1.41 m/s	

____	41.	As an object falls toward Earth,
a.	the object does not exert a force on Earth.	
b.	the object exerts a downward force on Earth.	
c.	Newton’s third law does not apply.	
d.	the upward acceleration of Earth is negligible because of its large mass.	

____	42.	The statement by Newton that for every action there is an equal but opposite reaction is which of his laws of motion?
a.	first	b.	second	c.	third	d.	fourth	

____	43.	Which are simultaneous equal but opposite forces resulting from the interaction of two objects?
a.	net external forces	c.	gravitational forces	
b.	field forces	d.	action-reaction pairs	

____	44.	As a basketball player starts to jump for a rebound, the player begins to move upward faster and faster until his shoes leave the floor. At the moment the player begins to jump, the force of the floor on the shoes is
a.	greater than the player’s weight.	
b.	equal in magnitude and opposite in direction to the player’s weight.	
c.	less than the player’s weight.	
d.	zero.	

____	45.	The magnitude of the gravitational force acting on an object is
a.	frictional force.	b.	weight.	c.	inertia.	d.	mass.	

____	46.	A measure of the quantity of matter is
a.	density.	b.	weight.	c.	force.	d.	mass.	

____	47.	A sled weighing 1.0 ´ 10 N is held in place on a frictionless 20.0° slope by a rope attached to a stake at the top. The rope is parallel to the slope. What is the normal force of the slope acting on the sled?
a.	94 N	b.	47 N	c.	37 N	d.	34 N	

____	48.	What are the units of the coefficient of friction?
a.	N	b.	1/N	c.	N	d.	no units.	

____	49.	A crate is carried in a pickup truck traveling horizontally at 15.0 m/s. The truck applies the brakes for a distance of 28.7 m while stopping with uniform acceleration. What is the coefficient of static friction between the crate and the truck bed if the crate does not slide?
a.	0.400	b.	0.365	c.	0.892	d.	0.656