Physics Exam 2018
A parachute slows a 0.3 kg falling toy from 8 m/s to 2 m/s. Determine the change in momentum of the falling toy.
-1.8 kg*m/s
example of negative acceleration
-accelerating west or south -deaccelerating/ stopping going north or east
gravitational potential energy is directly proportional to what
-mass -height -velocity
Which equipment is required to measure the energy of a rolling toy car at the top and bottom of a hill on a friction-less track in order to examine conservation of energy?
-scale/balance -ruler -stopwatch
A baseball thrown at 40 m/s has a momentum of 5.8 kg · m/s. Determine the mass of the baseball.
0.145 kg
A 0.1 kg arrow is shot from a bow at 60 m/s. The arrow hits a stationary 5 kg target and exits with a velocity of 30 m/s. What is the target's velocity after the arrow passes through it?
0.6 m/s
A 1 kg car is traveling at 5 m/s and it collides with a second of unknown mass that is at rest. After the collision the first car stops and the second car moves on at 5 m/s. Determine the unknown mass.
1 kg
A baseball (145 kg accelerating at 0.0069 m/s2) exerts how much force
1 newton
Two containers holding eggs are dropped from the same height, reaching the same maximum velocity as they fall. Both have the same mass and shape but container B has more padding. In container A the egg breaks and in container B the egg does not break. Which of the following correctly describe the containers? 1. The containers have the same change in momentum during the collision 2. The impulse during impact is the same for both containers 3. The impact force experienced by container A is greater because the impact time is lower
1, 2, 3
A person is walking at 1.3 m/s towards the back of an airplane that is traveling at 200 m/s. How fast would they appear to be moving to someone sitting in another seat on the plane?
1.3 m/s
if the distance between the center of 2 masses is doubled, the magnitude of the gravitational force btw them will be
1/4 its original magnitude
A person is walking at 2 m/s towards the back of an airplane that is traveling at 200 m/s. How fast would they appear to be moving to someone standing on the ground?
198 m/s
A person is sitting in their seat on an airplane that is traveling at 200 m/s. How fast would that person appear to be moving to someone standing on the ground?
200 m/s
A person movies at 1.0 m/s towards the front on an airplane that is traveling at 200 m/s. How fast would that appear to be moving to someone standing on the ground?
201 m/s
Book A has a potential energy of 50 Joules on a shelf. Book B has a potential energy of 90 Joules. Which of the following could explain their difference in potential energy?
Book B is on a higher shelf
equation for force
F=ma
A student gives a 25 N push against a 10 kg stationary cart for 3 seconds. Determine the final velocity of the cart.
Ft= mv v= Ft/m (since vi is 0) vf= Ft/m vf= (25)(3)/10 vf= 7.5 m/s
A 3,000 kg roller coaster car starts the bottom of a loop with a speed of 22 m/s. Determine the velocity of the car at the top of the loop if a net force pulls against the car with -31,000 N of force for 0.5 seconds as it rises to the top of the loop.
Ft= mv v= Ft/m vf - vi = Ft/m vf= Ft/m + vi vf= (-31,000)(0.5)/3,000 + 22 vf= 16.8 m/s
the value of the gravitational constant (G) was determined by:
Hendry Cavendish
A 0.4 kg object released from rest reaches 6 m/s as it falls to the floor 2 m below. What is the change in momentum of the object from release to just before impact?
J = mv J = m(v2-v1) J = 0.4(6-0) J = 2.4 kg*m/s
Determine the impulse delivered to a driver by a seat belt during a collision if the driver experiences a -13,000 N force for 0.4 seconds.
J= Ft J= (-13,000)(0.4) J= -5,200 Ns
Determine the kinetic energy of a 500 kg car moving at 28 m/s
KE = 1/2mv2 KE = 1/2(500)(28^2) KE = 196,000 J
A 0.50 kg soccer ball is kicked straight up into the air at 14 m/s. Determine the maximum height that it reaches.
KE = PE 1/2 mv2 = mgh h = v2/2g h= 14^2 / 2(9.8) h= 10 m
kinetic energy formula
KE=1/2mv^2
mechanical energy formula
ME = KE + PE
A 1 kg pendulum is found to have a velocity of 2 m/s when it is 0.1 meters above the lowest point in its swing. Determine the mechanical energy in the pendulum.
ME= ME + PE ME= 1/2mv2 + mgh ME= 1/2(1)(2)^2 + (1)(9.8)(0.1) ME= 2.98 J
What might demonstrate conservation of momentum?
Measure the mass and the velocity of two cars before and after they collide.
A 4 kg car which is traveling at 10 m/s collides with a 2 kg car which is moving in the same direction at 5 m/s. After the collision the heavier car is moving at 7 m/s and the lighter car is moving at 11 m/s. Determine whether momentum is conserved.
Momentum is conserved
who first proposed the Universal Law of Gravitation
Newton
power formula
P=W/t W= Fd
Determine the approximate elastic potential energy of a car's shock absorbing coil spring that is compressed 0.070 m and has spring constant of 35,000 N/m.
PE = 1/2kx2 PE = 1/2(35,000)(0.070)^2 PE = 86 J
A 0.6 kg basketball falls 3 meters from a hoop straight down to the ground. What approximate velocity is the ball moving with as it hits the ground?
PE = KE mgh = 1/2 mv2 v = sqrt(2gh) v = sqrt(2*9.8*3) v= 7.7 m/s
gravitational potential energy formula
PE = mgh
elastic potential energy formula
PEelastic = 1/2kx2
A 0.2 kg spring loaded dart is compressed against a spring 0.03 m and released horizontally. The spring constant is 56 N/m. How fast is the dart initially moving?
PEelastic = KEi 1/2kx2 = 1/2mv2 vi =sqrt(kx2 /m) vi =sqrt(56(0.03)^2/0.2) vi = 0.50 m/s
A 0.01 kg spring toy is compressed 0.02 m and released vertically. The toy is measured to reach 0.25 m in the air. Determine the spring constant for the toy.
PEelastic = PEg 1/2 kx2 = mgh k = 2mgh/x2 k = 2(0.01)(9.8)(0.25)/(0.02^2) k= 122.5 N/m
Determine the stored gravitational potential energy in a 300 kg roller coaster car that is 40 meters off the ground.
PEg = mgh PE = (300)(9.8)(40) PE = 117,600 J
A 0.1 kg arrow is shot at 120 m/s, a 4 kg cannonball is fired at 50 m/s, and a 1.2 kg model rocket launches with a velocity of 75 m/s. Determine which has the greatest momentum.
The cannonball
A cheetah spends 10 minutes sneaking up on an antelope, and then charges at it. What is likely the average and instantaneous velocity?
The cheetah's average velocity was 0.5 m/s and its instantaneous velocity when it charged was 30 m/s.
A 4 kg car which is traveling at 10 m/s collides with a 2 kg car, which is moving in the same direction at 5 m/s. After the collision the heavier car moves at 7 m/s and the lighter car moves at 11 m/s. Determine whether the collision is elastic or inelastic.
The collision is inelastic
A projectile is tossed from a catapult launcher that is powered by a rubber band. How does the elastic potential energy stored in the rubber band before launch compare to the initial kinetic energy of the projectile after launch?
The elastic potential energy is greater than the kinetic energy.
A toy car with a spring is pulled back, released, then rolls away horizontally. Which of the following best describes the energy in the system?
The energy is converted from elastic potential to kinetic and the total mechanical energy is constant.
Which makes the hypothesis below a testable, falsifiable hypothesis? "If you one object exerts a force on a second object, the second object will exert an equal and opposite force to the first object."
The hypothesis makes a prediction about variables, which can be objectively measured with empirical data.
Two toy cars are held together against opposite sides of a compressed spring. When they are released, the spring launches the toy cars in opposite directions. Which of describes the sum of the cars' momentum?
The resultant momentum of the two cars is zero before the separation and zero after the separation.
Calculate the work generated lifting a 5 kg dumbbell 1 meter.
W = Fd W = (ma)d W = (5)(9.8)(1) W = 49 J
A 300 kg car speeds up from 25 m/s to 35 m/s. Determine the input of work energy required to speed up the car.
W = KE W = 1/2mv2f - 1/2mv2i W = 1/2(300)(35^2) - 1/2(300)(25^2) W = 90,000 J
How much work energy is used to launch a 0.5 kg ball from the ground to 3 meters above the ground?
W= mgh W= (0.5)(9.8)(3)
What is the magnitude of centripetal acceleration for a 4 kg discus being thrown by an athlete with a 0.8 meter long arm if the discus is moving 14 m/s before being released?
a = v2/r a = 14^2 / 0.8 a = 245 m/s2
A car 10 m from the center of a turn is moving with a speed of 30 m/s. What is the magnitude of the car's centripetal acceleration?
a = v2/r a = 30^2 / 10 a = 900/10 a = 90 m/s2
A wild horse is trotting at a speed of 4.8 m/s when a loud noise spooks it . The horse then accelerates at a rate of 2.1 m/s2 and reaches a velocity of 16 m/s. Approximately how much distance does the horse travel while it is accelerating?
a = v2f - v2i / 2d d = v2f - v2i / 2a d = 16^2 - 4.8^2 / 2(2.1) d = 55.5 m
what could be used to measure the work energy given to an object
a force sensor and a meter stick
what causes an object to accelerate
an unbalanced force
which force vector refers to the push or pull that a person could give to an object
applied force
An unknown substance has a mass of 10.2 g. You measure the mass using an electronic balance and record the following measurements: 10.1 g, 10.2 g, 10.0 g, and 10.2 g. These measurements can be said to be:
both accurate and precise
the word "centripetal" means
center seeking
abbreviation for the metric prefix deka
da
A spring popper toy is set on the ground. Describe the initial transformation of energy in the system as the spring releases and the toy moves upwards.
elastic potential energy converts to kinetic energy
A nickel with a mass of 0.005 kg is placed on a spinning plate. The plate's rotation results in a centripetal acceleration of 1.25 m/s2. What is the magnitude of the centripetal force acting on the nickel?
f = ma f = (0.005)(1.25) f = 0.00625 N
A 30 kg child on a merry-go-round is riding a horse that is 8 m from the center of the merry-go-round. If the child has a tangential velocity of 3 m/s, what is the magnitude of the centripetal force on the child?
f = ma f = m (v2/r) f = (30)(3^2/8) f = (30)(9/8) f = 34 N
While you are heating a liquid over a flame, you accidentally end up catching your long sleeve shirt on fire. Which piece of safety equipment would be best to use in order to minimize injuries?
fire blanket
You are conducting a lab experiment and you are wearing safety goggles, a lab apron, gloves, and you have your hair pulled back. When you pick up a sharp projectile, it accidentally slips and cuts your hand. Which piece of safety equipment would be best to use to minimize injuries
first aid kit
push or pull acting on an object
force
what force acts on a projectile and on what axis
force of gravity on y-axis
why does a tennis ball lose energy as it rolls along the ground
friction does work opposing the ball's motion and decreases ME
while purchasing new tires, a truck driver wants tires that will allow him to be safe on slick roads. He should purchase tires that can provide the largest-
frictional force
A toy dart is compressed against a spring and is held stationary 2 meters above the floor. Which of the following are part of the total mechanical energy in the system at this instant?
gravitational potential energy and elastic potential energy
describe the energy transformation of a child sledding down a hill
gravitational potential energy is converted to kinetic energy
how is the inertia and mass of a boulder compared to a pebble
greater mass, greater inertia
the relationship between distance and gravitational force is an example of an ______________________
inverse-square law
how does tripling the compression of a spring affect its elastic potential energy
it will be 9 times greater
the unit Newton is equivalent to
kg*m/s^2
best scientific label for the phenomena known as gravity?
law
graph showing object undergoing acceleration
line curving upwards
A 3 kg cannonball is fired at 75 m/s from a 500 kg cannon. Determine the recoil velocity of the cannon.
m1v1 = -m2v2 v2 = -m1v1/m2 v2 = -(3)(75)/500 v2 = -0.45 m/s
Car A has a mass of 500 kg and is moving at 30 m/s. It collides head on with Car B, which has a mass of 600 kg and is moving at a velocity of -25 m/s. After the collision car A has a velocity of -30 m/s. Determine the final velocity of car B.
m1v1i + m2v2i = m1v1f + m2v2f v2f= m1v1i + m2v2i-m1v1f /m2 v2f = (500)(30)+(600)(-25)-(500)(-30) / 600 v2f = 25 m/s
A 2 kg toy car which is rolling at 5 m/s collides with a stationary 3 kg toy truck, and they bounce apart. Determine the total momentum in the system after the collision.
m1v1i + m2v2i = total final momentum (2)(5) + (3)(0) = total final momentum 10 kg*m/s
A 20 kg child runs at 3 m/s and jumps into a stationary 5 kg wagon. Determine the final velocity of the child and wagon.
m1v1i + m2v2i = vf (m1+m2) since v2i is 0 m/s m1v1i = vf(m1+m2) vf= m1v1i / (m1+m2) vf = (20)(3) / (20+5) vf = 2.4 m/s
kinetic energy is directly proportional to what
mass
Your friend pushes a textbook with a weight of 15 N toward you using 12 N of force. Friction between the book and the table exerts a force of 3 N to the left.
north: 15 N south: 15 N west: 3 N east: 12 N
While conducting a field lab, you are minorly injured. Although you do not believe that the injury is serious, you should still:
notify an adult of your injury
how much power is generated by a student pushing a box 2 meters along a ramp, with 12 N of force, in 3 seconds
p= W/t p= (Fd)/t p=(12)(2)/3 p= 8 watts
A force of 400 Newtons lifts a garage door 2.5 meters in 5 seconds. Determine the power generated by the opener.
p= W/t p= Fd/t p= (400)(2.5)/5 p= 200 W
Students release a ball from a horizontal compressed spring. They measure the initial velocity of the ball, its mass, and the compression of the spring. What other information do they need to determine whether energy was conserved during the launch?
spring constant
graph showing object accelerating at constant rate
straight horizontal line on acceleration/time graph
graph showing object in free fall on Earth
straight horizontal line on acceleration/time graph
graph showing negative velocity staying constant
straight line downward
graph showing positive velocity staying constant
straight line in upward direction
a line that touches a circle at only one point
tangent
why does a soccer ball speed up when kicked horizontally on level ground
the applied force does work on the ball increasing its kinetic energy
what can be demonstrated by measuring a falling object's height, mass, and final velocity
the energy in the system is conserved from the top of the fall to the bottom
main cause of Mars Climate Orbiter's destruction
the engineering teams didn't all use the same units
an object is in equilibrium when
the net force on the object is zero
the centripetal force acting on an object can be reduced by increasing...
the radius of the circular path
If the amount of force on an accelerating object is doubled, an object will accelerate at...
twice the original rate
first thing you should do when you are in a classroom laboratory, and something gets in your eye
use the eye wash station
If an object is traveling at a velocity of 37 m/s and has an acceleration of 0 m/s2, how far will it have traveled after 300 seconds?
v = d/t d = v x t d = 37 x 300 d = 11,100 m
A boulder rolls down from the top of a hill, at a constant velocity of 52.3 m/s. Approximately how long will it take the boulder to get to the bottom of the hill if the hill is 755 m tall?
v = d/t t = d/v t = 755/52.3 t = 14.4 s
average velocity equation
v(avg) = d/t
net force
vector sum of all forces acting on an object
a kinetic energy value that has quadrupled could be the result of what
velocity that was doubled
when working with hot liquids, what is the most important safety precaution
wear splash resistant safety goggles
A projectile is launched diagonally into the air and has a hang time of 24.5 seconds. Approximately how much time is required for the projectile to reach its apex?
24.5 / 2 = 12.25 sec
how are mental models and mathematical models related
a mathematical model objectively describes the relationship btw things and the mental model subjectively describes the relationship btw things
best definition of a scientific hypothesis
a statement in an "If... then..." format, which makes a falsifiable prediction.
acceleration equation
a=vf-vi/t
any change in speed or direction of an object
acceleration
why can science tell us about the consequences of pollution, but not what we should do about pollution?
because what we should do about pollution is a subjective political question
why can we talk about falsifiable scientific claims, and not provable scientific claims
because while you can show that a prediction is wrong, but even if your prediction is supported 1,000,000,000 times, the next time you test it, it could turn out to be wrong.
A football player kicks a ball horizontally off of a hill with an initial horizontal velocity of 42.0 m/s. It travels a horizontal distance of 59.2 m. How tall was the hill he kicked the ball off of?
d = vi(t) + 1/2 a(t^2) t = d/v t = 59.2/42 t = 1.41 s d = vi(t) + 1/2 a(t^2) d = 1/2 a(t^2) d = 1/2 (9.8)(1.41)^2 d = 9.74 m
A cannon ball is shot horizontally off a 86.5 m hill with an initial horizontal velocity of 105 m/s. What horizontal distance will the cannon ball travel?
d = vi(t) + 1/2 a(t^2) t = sqrt(2d/a) t = sqrt(2(86.5) / 9.8) t = 4.2 s d = vi(t) + 1/2 a(t^2) d = vt d = (105)(4.2) d = 441 m
An object at the top of an 89.4 meter tall cliff is launched horizontally with a horizontal velocity (VI X) of 33.6 m/s. What is the object's approximate hang time?
d = vi(t) + 1/2 at^2 t = sqrt(2d/a) t = sqrt(2(89.4)/9.8) t = 4.3 s
A family takes an airplane to go on vacation, and flies 1,700 kilometers to their destination, and 1700 kilometers back. How much distance have they traveled?
distance = 1700 + 1700 = 3400 km
If the mass of one object is doubled, its gravitational attraction to another object will-
double in magnitude
A 1,500 kg truck is parked 50 meters from a 1,000 kg van. What is the gravitational force between the pair?
f= G (m1m2 / d2) f= (6.67 x 10^-11)(1500x1000 / 50^2) f= 4.0 x 10^-8 N
What is the gravitational force between a 5.0 x 105 kg space station and a 3,500 kg asteroid at a distance of 450 m?
f= G(m1m2/d2) f= (6.67 x 10^-11)(5.0 x 10^5*3500 / 450) f= 5.76 x 10^-7 N
A force of 13 N is used to slide a 0.8 kg book across a table. What is the magnitude of the book's acceleration?
f= ma a= F/m f= 13/0.8 f = 16 m/s^2
How much force is needed to accelerate a 3kg object at a rate of 4m/s2?
f= ma f= (3)(4) f = 12 N
Use the textbook's weight (15 N) to determine its mass
f= ma m= f/a m= 15/9.8 m= 1.53 kg
If you took a 3 kg shovel from Earth to the moon, which of the following would change?
the shovel's weight
2.35 x 10^5 is equal to:
235,000
science has what limitations
-Science cannot make aesthetic or moral judgments -Science cannot ever be completely certain about its laws or theories
not allowable activities during a lab:
-drinking a beverage with/without a lid -eating a snack -using headphones
examples of centripetal force
-tension in a yo-yo string -gravitational force btw the Earth and moon
safety precautions for working for a projectile
-wear impact resistant safety glasses -avoid standing in front of launcher
safety precautions for working for a flame
-wear safety goggles -use appropriate gloves -tie back long hair
A person is sitting in their seat on an airplane that is traveling at 200 m/s. How fast would that person appear to be moving to someone sitting in another seat on the plane?
0 m/s
Which hypothesis would be most strongly supported by the scenario below? A student notices that as an object falls, it appears to fall faster as it gets closer to the ground. The student continues to make observations and notices that when an object falls from a greater height, that the object will be going faster when it reaches the ground.
If an object is dropped from a greater height, then it will have a greater speed upon impact.
SI unit for temperature
Kelvin (K)
An object is dropped from an airplane and takes 72 seconds to hit the ground. What is the magnitude of its VF Y ?
a = vf-vi/t vf = at vf = (9.8)(72) vf = 710 m/s
A car is traveling at 35 m/s and hits its brakes, slowing to a speed of 13 m/s over 5 seconds. In m/s2 , what is the car's acceleration during that time period?
a = vf-vi/t a = 13-35/5 a = -4.4 m/s2
A rocket starts at rest and then fires its engines for 10.5 seconds, accelerating at a rate of 300 m/s2. What will its approximate final velocity be?
a = vf-vi/t vf = a(t) + vi vf =300(10.5) + 0 vf =3150 m/s
Which of the following is the independent variable in the scenario below? "If you increase the height from which an object is dropped, then the object will increase its speed at a constant rate as it falls."
height object was dropped from
how should you dispose of a broken beaker
in a box labeled for broken glassware
resistance that an object has to changes in its motion
inertia
why is the standard picture of an atom with circles drawn for particles considered a conceptual model
it explains the concept of atomic structure
strongest model that can be made in science
law
best instrument for measuring distance
meter stick
what measuring system is the SI system based on
metric system
a number raised to 10^-3 has the same value as the metric prefix:
milli
example of a physical model
miniature catapult
in the case of gravitational force, the force is exerted..
mutually between any 2 objects regardless of their relative masses
A couch with a mass of 80 kg is pushed with a force of 72 N to the right. Friction exerts a force of 4 N to the left. The normal force and weight are 784 N in opposite directions. Using a free-body diagram, determine the magnitude of the acceleration of the couch
north: 784 south: 784 west: 4 east: 72 netforce = 784 -784 + 72 - 4 = 68 N f= ma a= f/m a= 68/80 a= 0.85 m/s^2
One mover pushes a couch toward the north with a force of 80N while another mover pushes toward the east with a force of 40 N. Which direction will the couch move and what is the magnitude of the resultant force?
northeast a2+b2 = c2 80^2 + 40^2 = c2 6400 + 1600 = c2 8000 = c2 c = 89.4 N
What term best describes the shape of the trajectory that a projectile takes as it moves through the air in free fall?
parabola
An object exerts a force of 10 N and you measure the force using a spring scale. The measurements you obtain are 12.1 N, 12.0 N, 11.9 N, and 12.1 N. Based on the given information, your measurements were:
precise but not accurate
Two dolphins push on a beach ball in the ocean. One pushes toward the east and one pushes toward the south. Which direction will the beach ball move?
southeast
graph showing object at rest
straight horizontal line
graph showing object not accelerating
straight horizontal line
A spaceship accelerates from a speed of 100 m/s to a speed of 1,100 m/s in 600 seconds. A car accelerates from a speed of 17 m/s to 50 m/s in 25 seconds. A train accelerates from a speed of 2 m/s to a speed of 8 m/s in 3.5 seconds. A toddler accelerates from a speed of 0 m/s to a speed of 2 m/s in 1 second. Which experienced the largest magnitude of acceleration?
toddler
centripetal force and centripetal acceleration are always directed...
toward the center of a circular path
tool used to measure mass of an object
triple beam balance
An object is dropped out of an airplane that is moving horizontally at 350 m/s and is 22,000 m above the ground. Ignoring friction, what will its approximate VF X be on impact?
vf= sqrt {vi^2 + 2ad} vf= sqrt {0^2+(2)(9.8)(22,000)} vf= sqrt {431,200} vf= 657 m/s t= vf - vi / a t= (657 - 0) / 9.8 = 67 seconds d= vi (t) + (1/2)(a)(t^2) d= (350)(67) + (1/2)(0)(67)^2 d= 23,450 vf= sqrt {vi^2 + 2ad} vf= sqrt {350^2+(2)(0)(23,450)} vf= sqrt {122,500} vf= 350 m/s
what is an example of normal force
your bed pushing up against you as you lay in it