Physics 107 Exam #1
What average net force is needed to accelerate a 1590 kg car to a speed of 24 m/s in a time of 7 s?
(1590 kg x 24 m/s)/ 7 = 5451 N*s
If you are traveling at an average speed of 60 miles per hour, how long will it take to go from mile marker 1 to mile marker 7?
(7mi-1mi) = 6mi/60mph = .1/60minutes = 6 minutes
kilogram
1000 Grams
Kilometer
1000 Meters
What impulse is needed to stop a 1000 kg car traveling at 22 m/s?
1000 kg * 22 m/s = 22000 N*s
Size of Red Blood Cell
10^-13 kg
Size of Bactorium
10^-15 kg
size of protons and neutrons to the size of the visible universe
10^41
Vector
a physical quantity that has a DIRECTION associated with it as well as a MAGNITUDE. FORCES are vectors. WEIGHT is a force and is therefore also a vector. Velocity is a vector: speed plus direction give us the velocity of an object
Scalar
a quantity that DOES NOT have a DIRECTION associated with it, only a MAGNITUDE in some appropriate units systems. Mass is a scalar. So is speed.
Light Year
a unit of distance equal to the distance that light travels in one year (about 5.88 trillion miles or 9.46 trillion kilometers)
Average acceleration
Change in velocity/time Units: m/s2
Average velocity
Displacement of object/time taken Units: m/s
A 6 kg ball has been thrown vertically upward. If we ignore the air resistance, what are the direction and size of the net force acting on the ball while it is traveling upward?
Down; 6 x 10 (aka g) = 60 N
If you were located halfway between the Earth and the Moon, what acceleration would you have toward Earth?
Earth is 30 radii away from the moon 1/30^2 = 1/900 = .00111 .00111 x g = .011
A collision in which kinetic energy is conserved is called what?
Elastic
Newton's Law of Universal Gravitation - the inverse square law
F = g*(m1xm2/r^2)
What does the law of conservation of momentum tell us about collisions?
The total momentum in the system does not change because of a collision.
Why don't the two forces in Newton's third law cancel each other?
They act on two different objects
Newton's Third Law
To every force or action, there is an equal and opposite reaction
How is an arrow shooting off a vector?
Vector needs magnitude and direction An arrow's length is the magnitude and the way it goes after shooting is its direction.
How are speed and velocity related?
Velocity specifies both the speed and the direction of a moving object.
Phenomenon
a fact, occurrence, or circumstance observed or observable
BASE UNITS
a minimum set of arbitrarily defined units from which all other units can be derived. Examples of base units: Meter, Kilogram, Second, etc.
DERIVED UNITS
derived from the base units Example: M/s, Square Meter, etc.
Microscopic Scale
is the scale of objects and events smaller than those that can easily be seen by the naked eye, requiring a lens or microscope to see them clearly
Momentum is measured in what unit?
kgm/s
units of the metric system
kilograms, micrometers, and milliseconds
In Newton's second law, mass and acceleration for constant force are which of the following?
inversely proportional
Instantaneous velocity
is given by the slope of the tangent to a position against time graph.
Instantaneous acceleration
is given by the slope of the tangent to a velocity against time graph
Inertia
tendency of a body to maintain its state of motion (No unit, not quantitative)
net force always points in the same direction as
the acceleration
If the pole-vaulter were to land on concrete rather than on a cushion, the impulse that stops the fall would be what?
the same because impulse is the change in momentum of the object
If a net external force acts on a system, what will change?
the sum of the momenta of all objects in the system
elastic collision of two objects
total momentum is conserved, and the total kinetic energy after the collision is the same as the kinetic energy before the collision.
Centripetal acceleration
v^2/r where V = Velocity and R = Radius
linear momentum of a moving object is
velocity x mass
Aristotle believed that the speed at which objects fall depends on...
weight and the medium they fall through
A father (m = 71 kg) and son (m = 39 kg) are standing facing each other on a frozen pond. The son pushes on the father and finds himself moving backward at 3 m/s after they have separated. How fast will the father be moving?
(Mfather)(VFather) = (Mson)*(Vson) (71 kg)(x) = (39 kg)(3) x = (117)/(71) = 1.65 m/s
You throw a ball straight up at 20 m/s. How many seconds elapse before it is traveling downward at 10 m/s
-10 = -10t +20 -30 = -10t t = 3 seconds (note: g is actually equal to 9.8)
A toy car has a kinetic energy of 9 J. What is its kinetic energy after a frictional force of 0.5 N has acted on it for 5 m?
.5N x 5m = 2.5 9 J - 2.5 = 6.5 J
Unit of force:
1 Newton
1 newton =
1 kg/m^2
Megaton is how many tons?
1 million tons
Far away is sun
1.5 * 10^11 meters
Acceleration of a falling object
10 m/s
Thickness of hair
100 Micrometers or 1x10^-4
A boxcar traveling at 14 m/s approaches a string of 2 identical boxcars sitting stationary on the track. The moving boxcar collides and links with the stationary cars and they all move off together along the track. What is the final speed of the cars immediately after the collision?
14 - 3V = Final Speed 14/3= V V = 4.6 m/s
Centimeter
1X 10^-2 Meters
Nanometer
1X10^-9 Meters
Millimeter
1x10^-3 Meters
Micrometer
1x10^-6 Meters
Megameter
1x10^6 Meters
A 2 kg ball is thrown straight up in the air. What is the net force acting on the ball when it reaches its maximum height? What is the ball's acceleration at this point?
2 x 10 (aka g) = 20 N 20 N / 2 = 10 m/s^2
What is the acceleration of a 470 kg buffalo if the net force on the buffalo is 1350 N
2.87 m/s^2
If a runner can average 4.6 mph, can he complete a 100 mile supermarathon in less than 24 h? What would his time be?
24 hours / 4.6 mph = 21.7 hours to complete 100 miles
Far away is moon
3.84 x 10^8 Meters
The acceleration due to gravity on Titan, Saturn's largest moon, is about 1.4 m/s2. What would a 40 kg scientific instrument weigh on Titan?
40 kg * 1.4 m/s^2 = 56 N
Size of Virus
Nanometers
The gravitational force between two very large metal spheres in outer space is 56 N. How large would this force be if the mass of each sphere were quadrupled?
56 * 16 = 896
What is the Earth's gravitational force on you when you are standing on the Earth and when you are riding in the Space Shuttle 350 km above the Earth's surface? Answer as a fraction of the surface gravity of Earth. (The Earth's radius is 6400 km.)
6400^2 / (350 + 6400)^2 = .89
What is the ratio of the gravitational force on you when you are 6300 km above the Earth's surface versus when you are standing on the surface? (The Earth's radius is about 6400 km.)
6400^2 / (6300 + 6400)^2 = .25
A woman with a mass of 65 kg climbs a set of stairs that are h = 2 m high. How much gravitational potential energy does she gain?
65 x 20 m/s (assuming that g is 10) = 1300 J
Far away is galaxy
70000 Light Years
How do velocity and acceleration differ?
Acceleration is the rate of change of velocity, while velocity is the rate of change of displacement.
Net force acting in same direction
Addition
A rock is dropped into an abandoned mine and a splash is heard 7 s later. Assuming that it takes a negligible time for the sound to travel up the mine shaft, determine the depth of the shaft and how fast the rock was falling when it hit the water
Fast rock was going: 7 x 10 (10 is aka g) = 70 m/s Depth of shaft = .5*(70 x 10) = .5*(490) = 245 meters
A baseball is hit with a horizontal speed of 16 m/s and a vertical speed of 18 m/s upward. What are these speeds 3 s later?
Horizontal Speed: 16 m/s since speed stay constant horizontally Vertical Speed: 18 + (g*3) = 18 -30 = -12 m/s
When an item has been launched into orbit, what happens?
It continues to fall but its path never reaches the ground.
What do we know about the direction of momentum?
It has the same direction as the object's velocity
What is true of the rock as it falls after being dropped from a great height?
Its speed increases until it reaches a constant value, but its acceleration decreases gradually to zero.
Unit for Kinetic Energy
Joule
What is the kinetic energy of a 1000 kg sports car traveling down the road with a speed of 29 m/s?
KE = .5(M)(v^2) KE = .5(1000)(29^2) KE = 420500
Newton's First Law
Masses (chunk of matter) remain at rest or move in a straight line at constant speed unless a resultant force act upon them.
Earth in miles (Given: 10^7 meters)
Meters to Mile: 3.3 feet in 1 meter and 5280 feet in 1 mile (10^7 / 3.3) / 5280 = 5739.21 Miles or 6000 miles with order of magnitude.
astronaut's experiment with the hammer and the feather illustrates what
Objects of different size, shape, and mass fall at the same rate in a vacuum
What results when the net force on an object increases
Proportionally increased acceleration.
Net force acting in right angles of each other
Pytrhagroem theorem
Atomic Scale
Scale used to measure atoms
Net force acting in opposite direction
Subtraction
According to Newton's theory of gravity, why does the Moon have a much lower acceleration than a falling object on Earth
The Moon is farther away from Earth's center than the object falling at Earth's surface.
If you are whirling a ball on a string and you suddenly cut the string, what happens?
The ball goes off in a straight line based on where it was heading when the string was cut.
If the momentum of one object changes in a system that is subject to no net external force, what else must happen?
The momenta of the other objects in that system change to cancel out the first change
If a moving object hits a still object, what happens to the momentum of the moving object?
The momentum of the moving object is decreased by the amount of momentum the stationary object picks up at the time of the collision.
Newton's Second Law
The resultant force acting on a body is a vector equal in magnitude and direction to the product of its mass (a scalar) and its acceleration (a vector). (This tells you how to measure the force). The equation that relates force to mass and acceleration is: F = ma (Force = Mass x acceleration). This is also used to define the UNIT of force.
A 42 kg person on a merry-go-round is traveling in a circle with a radius of 2 m at a speed of 6 m/s. a) What acceleration does the person experience? b) What is the net horizontal force? c) How does it compare with the person's weight?
a) (6^2)/2 = 36/2 = 18 m/s^2 b) (42 kg x 6^2) /2 = 1512/2 = 756 N c) Acceleration/ Gravity = (18m/s^2 / 9.8m/s) = 1.84
A ball thrown vertically upward, at the top of its path (just before it starts to fall) has which of the following
an instantaneous speed of zero
How small a time interval is needed for a good calculation of instantaneous speed?
an interval short enough so that the answer won't change very much if you use a shorter one
a satellite orbiting the Earth is undergoing what?
circular motion
atomic clock
counts (as do more conventional clocks) the number of times a periodic (or repeating) phenomenon has occurred
metric prefixes is in order from smallest to greatest nano tera femto mega centi
femto, nano, centi, mega, tera
Order of magnitude
for a quantity is its value rounded off to the nearest power of ten
Weight
force exerted on an object by the earth's gravitational pull (attraction) Weight is a FORCE, so that it has a direction as well as magnitude, and its unit is the same as the unit of force. In the "everyday" system, this is the pound (lb.), but in formal scientific and engineering applications, we use the Newton (N).
Acceleration due to gravity
g (it varies with location, but the average value is often quoted as 9.80 m/s2; in all calculations, use the approximate value of as 10.0 m/s2)
Units of acceleration
m/s^2
Mass
measure of the amount of matter in a body = quantitative measure of body's inertial properties Unit: kg
Centripetal force
mv^2/r where M = Mass and V = Velocity and R = Radius
Nanoscale
of or relating to microscopic particles of matter, devices, etc., that are measured in nanometers or microns:
units of the U.S. customary system
ounces, inches, and seconds
Air resistance
resistance offered by the air to the motion of an object
What is terminal speed affected by?
size, weight, and shape
