Physics Exam 1
What is the acceleration of a car moving along a straight road that increases its speed from 0 to 100 km/h in 10 s?
10 km/h·s
A tow truck exerts a force of 3000 N on a car, which then accelerates at 2 m/s2. What is the mass of the car?
1500 kg
What is the instantaneous velocity of a freely falling object 15 s after it is released from a position of rest?
150m/s
The mass of a ball moving at 3 m/s with a momentum of 48 kg m/s is
16 kg.
What is inertia?
Inertia is the tendency of a body to maintain its state of motion in the absence of applied forces.
Newton's first law is often called the law of ____; Newton's second law is the law of ____; and Newton's third law is the law of ____.
Inertia, acceleration, action -reaction
At very low speeds for small particles, air resistance (F) is approximately proportional to the speed (v) and can be expressed in the form F = b v. Perform a dimensional analysis and identify the unit for the coefficient b.
Ns/m
Select the correct equations that show that 35 W of power is required to give a brick 245 J of PE in a time of 7 s .
P=W/t=(245J)/(7s)=35W
Why is it advantageous to roll with the punch in boxing?
Rolling with the punch increases contact time, which decreases the force.
A different scaffold that weighs 400 N supports two painters, one 500 N and the other 400 N. The reading in the left scale is 800 N. What is the reading in the right-hand scale? Express your answer to two significant figures and include the appropriate units.
T=500 N
As you increase your push on a stationary crate, will friction on the crate increase also?
The friction force increases and is opposite in direction to your push.
How does a helicopter get its lifting force?
The helicopter exerts downward forces on air; the reaction forces of the air on the helicopter are upward and called lift.
An object cannot remain at rest unless which of the following holds?
The net force acting on it is zero.
If a block is moving to the left at a constant velocity, what can one conclude?
The net force applied to the block is zero.
If a block is moving to the left at a constant velocity, what can one conclude? (More than one statement may be correct).
The net force applied to the block is zero. There may be a force to the right.
What is the net force on an object in either static or dynamic equilibrium?
The net force is zero.
What is the main difference between speed and velocity?
Velocity includes a direction, but speed does not.
As you read this in your chair, how fast are you moving relative to the chair? Relative to the Sun?
You are not moving relative to the chair, but you are moving over 100,000 km/h relative to the Sun.
Once the crate is sliding, how hard do you push to keep it moving at constant velocity?
You push with a force equal to and opposite the dynamic friction force.
An object in linear motion has zero speed at a particular instant. At that moment, it must have
Zero velocity
A massive block is being pulled along a horizontal frictionless surface by a constant horizontal force. The block must be __________.
moving with a constant nonzero acceleration
A ball rolling down an inclined plane each second picks up ______.
the same amount of speed each second
Emily holds a banana of mass m over the edge of a bridge of height h. She drops the banana and it falls to the river below. Use conservation of energy to find the speed of the banana just before hitting the water.
v = √2gh
even on a rough surface the force of static friction may be
zero
A cart maintains a constant velocity of 100 m/s for 10 seconds. During this interval its acceleration is
zero.
What is the gain of potential energy of the barbell when it is lifted to this height?
ΔU = 1300 J
A ball is projected 125 meters straight upward and then falls the same distance back to its starting point. Neglecting air resistance, its total time in the air is about
10 s
How far will it fall during this time?
1100m
A body of mass 6 kg is acted on by a force so that its velocity changes from 3 m/s to 5 m/s. What is the change in momentum?
12.0 N⋅s
How far does a horse travel if it gallops at an average speed of 25 km/h for 30 min?
12.5 km
Forces of 3.2 N and 4.2 N act at right angles on a block of mass 1.9 kg . Find the acceleration of the block.
2.8 m/s2
A 1-kg falling object encounters 5 N of air resistance. Its acceleration is
5.00 m⋅s−2
Exactly what is it that enables an object to do work?
Energy
What is the distance fallen for a freely falling object 1 s after being dropped from a rest position? What is the distance for a 4-s drop?
It falls 5 m in 1 s and 80 m in 4 s.
What is the gain in speed per second for a freely falling object?
It gains approximately 10 m/s.
What is the acceleration of a falling object that has reached its terminal velocity?
The acceleration is 0.
Consider a person walking from point A to point B. The distance the person walks can be greater than the magnitude of her displacement, but the magnitude of the displacement can never be greater than the distance she runs.
True
Calculate the work done in lifting a 580-N barbell 2.2 m above the floor.
W = 1300 J
Which varies with location, mass or weight?
Weight varies with location, but mass does not.
It is correct to say that impulse is equal to
a corresponding change in momentum.
What is the unit of work?
joule
A 1-kg box is at rest on a horizontal floor. Bill pushes the box with a horizontal force of 3 N but is not able to set it in motion. Select ALL the correct answers. Use g = 10 m/s2.
w=10N fs=3N
A crate sits at rest on a factory floor. Friction between the crate and floor occurs _______.
when the crate is pushed horizontally, whether sliding or not.
The ratio circumference/diameter for all circles is π. What is the ratio force/mass for freely falling bodies?
The ratio is g.
Why doesn't a heavy object accelerate more than a light object when both are freely falling?
The ratio of the weight to mass is the same for all objects in the same locality.
What is the resultant of a pair of one pound forces at right angles to each other?
The resultant is a force of 1.41 pounds in a direction bisecting the 90-degree angle between the two vectors.
The acceleration of free fall is about 10 m/s2. Why does the seconds unit appear twice?
The second appears once in the denominator of the unit for speed and once for the interval of time.
What is the speed acquired by a freely falling object 5 s after being dropped from a rest position? What is the speed 6 s after?
The speed is 50 m/s after 5 s and 60 m/s after 6 s.
Railroad car A rolls at a certain speed and makes a perfectly elastic collision with car B of the same mass. After the collision, car A is observed to be at rest. How does the speed of car B compare with the initial speed of car A?
The speed of car B is equal to the initial speed of A.
What relationship did Galileo discover about a ball's acceleration and the steepness of an incline? What acceleration occurs when the plane is vertical?
The steeper the incline, the greater the acceleration. On a vertical incline, the ball is in free fall.
Consider Nellie hanging at rest in Figure 2.11. If the ropes were vertical, with no angle involved, what would be the tension in each rope?
The tension in each rope would be half of the gravity force.
Lucy Lightfoot stands with one foot on one bathroom scale and her other foot on a second bathroom scale. Each scale reads 360 N . What is Lucy's weight? Express your answer with the appropriate units.
W=720 N
the force of kinetic frictions always opposes the
direction of motion
Consider a 100-kg box of tools in the locations A, B, and C. From greatest to least, rank the masses of the 100-kg box of tools.
earth, jupiter, moon are equal
The total momentum of a flock of identical birds could be zero only if the birds are
flying in different directions.
The standard symbol for the acceleration of gravity is
g
What is the magnitude of the impulse on an 8.2-kg ball rolling at 3.0 m/s when it bumps into a pillow and stops?
impulse = 25 N⋅s
An impulse can be increased by
increasing the force or increasing the time interval.
The speedometer of an automobile reads
instantaneous speed.
A ball is tossed with enough speed straight up so that it is in the air several seconds. Assume upward direction is positive and downward is negative. -What is the velocity of the ball when it reaches its highest point? -What is its velocity 1 s before it reaches its highest point? -What is the change in its velocity during this 1-s interval? -What is its velocity 1 s after it reaches its highest point? -What is the change in velocity during this 1-s interval? -What is the change in velocity during the 2-s interval? -What is the acceleration of the ball during any of these time intervals? -What is the acceleration of the ball at the moment the ball has zero velocity?
-0 m/s -10m/s --10m/s --10m/s --10m/s --20m/s --10m/s2 --10m/s2
Which of the following quantities has units of a velocity? (There could be more than one correct choice.)
-120 m/s 9.8 m/s downward
A rock is dropped from a height of 125 m above ground. Use g = 10 m/s2 in all calculations. -What is the distance traveled during the third second? -What is its speed after 3 seconds? -How long does it take the rock to hit the ground? -What speed does the rock have when it hits the ground?
-25 m -30 m/s -5 s -50 m/s
A 70-kg box is at rest on a horizontal surface. Select the correct statements (there can be more than one):
-Its weight is about 700 N and points down. -Its inertia is greater than that of a box weighing 500 N. -Its acceleration is zero.
The earliest and most influential Greek philosopher was Aristotle, who among many contributions taught that
-he four elements are earth, water, air, and fire. -violent motion requires a sustained push or pull. -all motion is either natural or violent.
-An athlete does not come to rest immediately after crossing the winning line due to the -When an object is at rest,
-inertia of motion -several forces balancing each other may be acting on it.
An object in mechanical equilibrium is an object
-moving with constant velocity. -at rest. -having no changes in velocity
The force on a dropped apple hitting the ground depends upon
-the time of contact with the ground. -the speed of the apple just before it hits. -whether or not the apple bounces.
A cart of mass 1.0 kg moving at 1.0 m/s to the right collides with another cart, of mass 0.50 kg, moving at 2.0 m/s in the opposite direction. Upon collision, the two carts remain coupled. What is the velocity (i.e., speed and direction) of the system of two carts after the collision?
0
An object of mass 1 kg is sliding with a constant velocity of 4 m/s on a frictionless horizontal table. The force required to keep the object moving with the same velocity is
0 N
Two people each pull with 300 N on a rope in a tug of war. What is the net force on the rope?
0 N
A 14,000-kg boxcar is travels at 1.50 m/s along a horizontal track when it suddenly hits and couples with a stationary 10,000-kg boxcar. What is the speed of the cars just after the collision?
0.875 m/s
Consider a mass of 1 kg accelerated 1 m/s2 by a force of 1 N. Find the acceleration for a force of 2 N acting on 2 kg.
1 m/s^2
Given the measurements 10 m, 10 m/s, and 10 m/s2, which is a measure of speed, which is a measure of distance, and which is a measure of acceleration?
10 m is distance, 10 m/s is speed, and 10 m/s2 is acceleration.
The tension in the string connected between the two blocks is M1= 2kg M2=4kg F1=20 N F2=10 N -The acceleration of the two blocks is -If the blocks are initially at rest, their speed after 1 s is -If the blocks are initially at rest, the distance traveled in 1 s is
13.3 N -1.66 m/s^2 -1.66 m/s -.830 m
Two blocks are connected with a rigid rod, as shown. What is the acceleration of the 3 kg mass when the acceleration of the 2 kg mass is 2 m/s2? M1=3kg M2=2kg Force=10N to right
2 m/s^2
The average force necessary to stop a hammer with momentum p Ns in 0.5 s is
2p N
The speed of a 4-kg ball with a momentum of 12 kg m/s is
3 m/s.
A motorcycle of mass 100 kilograms slowly rolls off the edge of a cliff and falls for three seconds before reaching the bottom of a gully. Its momentum upon hitting the ground is
3,000 kg m/s.
Nellie pulls on a 10-kg wagon with a constant horizontal force of 30 N. If there are no other horizontal forces, what is the wagon's acceleration?
3.0 m/s2
Convert 3 cm into meters.
3.00×10−2 m
What is the average speed in kilometers per hour of a horse that gallops a distance of 15 km in a time of 30 min?
30 km/h
A person starts from the origin (x = 0), goes along the x-axis to x1 = 10 m and then returns along the same line to the point x2 = -10 m. The distance and the displacement for this trip are
30 m, -10 m
Two people each pull with 300 N on a rope in a tug of war. What is the net force on the rope?
300 N
Some animal is running in a straight line. If we double both the mass and the speed of the animal, the magnitude of its momentum will increase by what factor?
4
Calculate the impulse due to a force of 4.5 N that lasts for 1.4 s.
6.3 kg⋅m/s
Lucy Lightfoot stands with one foot on one bathroom scale and the other foot on a second bathroom scale. Each scale reads 300 N. What is Lucy's mass?
60 kg
An 80-km/h airplane flying against a 10-km/h head wind has a groundspeed of
70 km/h.
What is its average velocity during this 15-s interval?
75m/s
How does acceleration depend on mass?
Acceleration is inversely proportional to mass.
How does acceleration depend on the net force?
Acceleration is proportional to the net force.
(Figure 1) The auto in the sketch moves forward as the brakes are applied. A bystander says that during the interval of braking, the auto's velocity and acceleration are in opposite directions. Do you agree or disagree?
Agree
What exactly is meant by a "freely falling" object?
An object in free fall falls under gravity alone with no friction.
A block of mass 2kg is acted upon by two forces: 3N (directed to the left) and 4N (directed to the right). What can you say about the block's motion?
It could be moving to the left, moving to the right, or be instantaneously at rest.
Fill in the blanks: The Standard International unit for mass is _____. The Standard International unit for force is _____.
Mass is kilograms; force is newtons.
If the mass of a sliding block is somehow tripled at the same time the net force on it is tripled, how does the resulting acceleration compare with the original acceleration?
The acceleration remains the same.
If the net force acting on a sliding block is somehow tripled, what happens to the acceleration?
The acceleration triples.
Two cars are raised to the same elevation on service-station lifts. If one car is twice as massive as the other, compare their gains of potential energy.
The car with twice the mass has twice the gain of potential energy.
If you push on a crate with a horizontal force of 100 N and it slides at constant velocity, what is the magnitude and direction of the frictional force acting on the crate?
The frictional force on the crate is 100 N opposite the direction of motion.
When traveling twice as fast your kinetic energy is increased _______.
by a factor of four.
If no external forces act on a moving object, it will
continue moving at the same speed.
While a car travels around a circular track at a constant speed, its
inertia is zero. acceleration is zero. velocity is zero. none of the above(correct answer)
Air resistance on a parachutist at terminal speed _______.
is greater for a heavier person
The Joule can be expressed in terms of fundamental SI units as:
kg∗m2∗s−2
Neglecting air resistance, once a tossed ball leaves your hand
only the force due to gravity acts on it.
The quantity that is called impulse can be measured by the _______.
product of force and time.
When you walk, you push on the floor to the left and the floor
pushes you to the right.
When hitting a tennis ball with your racquet, the force on the ball has the same magnitude as the force on the _______.
racquet
Four physical quantities (A, B, C, D) are related to each other according to A = B x C/D. If B is measured in kg, C in m/s, and D in N, the unit of A is (your answer should contain only fundamental SI units):
s
A hamster has an acceleration of 3 m/s2 . Select the correct equations that show that the hamster travels a distance of 37.5 m in 5 s .
s=a⋅t2/2=(3m/s2)⋅(5s)2/2=37.5m
Which of the following is not a vector quantity?
speed
