physics midterm
9) As a 70-kg person stands at the seashore gazing at the tides (which are caused by the Moon), how large is the gravitational force on that person due to the Moon? The mass of the Moon is 7.35*10^22 kg, the distance to the Moon is 3.82*10^8 m, and G=6.67*10^-11 N * m^2/kg^2.
0.0024 N Fg=G*m(person)*Mm/r^2 = (6.67*10^-11)(70)(7.35*10^22)/(3.82*10^8)^2 = 0.00235 = 0.0024 N
Consider a motorcycle of mass 150kg, one wheel of which has a mass of 10kg and a radius of 30 cm. What is the ratio of the rotational kinetic energy of the wheels to the total translational kinetic energy of the bike? Assume the wheels are uniform disks.
0.067:1
The moment of inertia of a solid cylinder about its axis is given by 0.5MR^2. If this cylinder rolls without slipping, the ratio of its rotational kinetic energy to its translational kinetic energy is what?
1:2
A heavy bank vault door is open by the application of a force 3.0 X 10^2 N directed perpendicular to the plane of the door at a distance of .8 m from the hinges what is the torque
240 N•m
In seven seconds a car accelerates uniformly from rest to a velocity at which its wheels are turning at 6 rev/sec. If the tires of the car has a diameter of 42 cm and they rolled on the ground without slipping how far did the car go in those seven seconds
28 m
8) One way that future space stations may create artificial gravity is by rotating the station. Consider a cylindrical space station 380 m in diameter that is rotating about its longitudinal axis. Astronauts walk on the inside surface of the space station. How long will it take for each rotation of the cylinder if it is to provide "normal" gravity for the astronauts?
28 s Find T using V=2(pie)R/T. 1) solve for V using Ac=V^2/R. = v^2=Ac/r = sq rt(9.8/190m) = 43.17 m/s. 2) 2) plug into first equation: 43.17=2(pie)(190m)/T = (solve for T) 27.65 s
Two are applied perpendicular to a door at the doorknob. The first is 2x as large as the second. What is the ratio of torque from the first force to the second?
2:1 (so 2)
Consider two uniform solid SPHERES where both have the same diameter, but one has twice the mass of the other. What is the ratio of the moment of inertia from the larger to the smaller?
2:1, so 2
If the torque required to loosen a nut on a wheel has a magnitude of 400 N M and the force exerted by mechanic is 133 N how far from the knot must the mechanic apply the force
30.1 cm
Short answer #1: A Ferris wheel has radius 5.0 m and makes one revolution every 8.0 s with uniform rotation. A person who normally weighs 670 N is sitting on one of the benches attached at the rim of the wheel. What is the apparent weight (the normal force exerted on her by the bench) of the person as she passes through the highest point of her motion?
460 N V=2[pi]r/T = 2[pi](5.0)/8.0) = 3.927 m/s Ftotal = Fn + mg = ma(centripetal) = mv^2/r Use --> Fn+mg=mv^2/r --> [m=(670/9.81) = 68.3 g kg] Fn=-mg + mv^2/r = -670 N + (68.3 kg*3.927^2)/5.0 = -459 N [Why do I get a negative number?]
A ball is thrown vertically upward with a speed v/ An identical second ball is thrown upward with a speed 2v (twice as fast). What is the ratio of the maximum height of the second ball to that of the first ball?
4:1
Consider two uniform solid SPHERES where both have the same mass, but one has twice the diameter of the other. What is the ratio of the moment of inertia from the larger to the smaller?
4:1 - so 4 - because the formula for I is mr^2, and twice the diameter = twice the radius, so that radius squared would be 4 times larger than the smaller one. So you know like. Math. *shudders* On second thought, just memorize the number 4 like that's all you gotta know man, that's all you gotta know.
In seven seconds a car accelerates uniformly from rest to a velocity at which its wheels are turning 6 rev/sec. what was the angular acceleration of the cars wheels
5.4 rad/sec^2
Consider two uniform solid SPHERES where one has twice the mass and twice the diameter of the other. What is the ratio of the moment of inertia from the larger to the smaller?
8...yeah I'm not doing the math it's just 8, m8
7) A 1000-kg car is moving at 30 m/s around a horizontal unbanked curve whose diameter is 0.20 km. What is the magnitude of the friction force required to keep the car from sliding?
9000 N (mew)mg=mv^2/r mew=900/(100*9.81)=0.917 F fric.= 0.917*1000*9.81=9000N
A golf ball traveling 3.0 m/s to the right collides in a head-on collision with a stationary bowling ball in a friction-free environment. If the collision is almost perfectly elastic, the speed of the golf ball immediately after the collision is A) slightly less than 3.0 m/s B) slightly greater than 3.0 m/s D) equal to 3.0 m/s D) much less than 3.0 m/s
A
A sailboat of mass m is moving with a momentum of p. How would you represent its kinetic energy in terms of these two quantities? A) p^2/(2m) B) 1/2mp^2 C) mp D) mp/2
A
Two cars collide head-on on a levee friction-free road. The collision was completely inelastic and both cars quickly came to rest during the collision. What is true about the velocity of this system's center of mass? A) It was always zero B) It was never zero C) It was not zero, but ended up zero D) none of the above
A
Two objects collide and bounce off each other. Linear momentum A) is definitely conserved B) is definitely not conserved C) is conserved only if the collision is elastic D) is conserved only if the environment is frictionless
A
12) As shown in the figure, a given force is applied to a rod in several different ways. In which case is the torque about the picot P due to this force the greatest?
A (straight up)
Consider a rigid, dead body that is rotating as it floats in a secluded pool of blood and swamp water. What, aside from the tragic state of the situation, what is an accurate statement?
All points on the body are moving with the same angular velocity.
A child is writing a merry-go-round which is accelerating. What is the relationship between the angular speed w and the angular acceleration a of the merry-go-round went to tangential and centripetal acceleration of the child are equal
Alpha=omega ^2
If you want to open a swinging door with the least amount of force where should you push on the door
As far from the hinges as possible
A red ball with a velocity of +3.0 m/s collides head-on with a yellow fall of equal mass moving with a velocity of -2.0 m/s. What is the velocity of the yellow ball after the collision? A) zero B) +3.0 m/s C) -2.0 m/s D) 5.0 m/s
B
In a game of pool, the white cue ball its the #9 ball and is deflected at a 35 degree angle to the original line of motion. What is the angle of deflection below the original line of motion for the #9 ball? A) 35 B) 55 C) 75 D) 90
B
Two objects collide and stick together. Kinetic energy A) is definitely conserved B) is definitely not conserved C) is conserved only if the collision is elastic D) is conserved only if the environment is frictionless
B
10) The figure shows scale drawings of four objects, each of the same mass and uniform thickness, with the mass distributed uniformly. Which one has the greatest moment of inertia when rotated about an axis perpendicular to the plane of the swaying at point P?
B (hollow cylinder = MR^2, solid cylinder = 1/2MR^2, rectangle = 1/3ML^2)
A boy and a girl are riding on a merry-go-round that's turning at a constant rate. The boy is near the outer edge like a daredevil, and the girl is closer to the center because she's smart. Who has the greater angular displacement?
Both have the same non-zero angular displacement
A boy and a girl are still riding on a merry-go-round that's turning at a constant rate. The boy is near the outer edge l ready to fall off, and the girl is closer to the center because she's recording a final Vine of the situation (RIP Vine 2013-2017). Who has the greater angular speed?
Both have the same non-zero angular velocity.
A boy and a girl are now again riding on a merry-go-round, which is turning at a constant rate, because they're young and make stupid decisions like continually nearly killing themselves on a massive human centrifuge of terror. The boy is hanging over the outer edge passed out and hitting his head on every rock they spin past, and the girl is in the center sitting in a pile of her own vomit and tears. Who has the greater tangential acceleration?
Both have zero tangential acceleration
A boy and a girl or writing a merry-go-round which is turning at a constant rate. The boy is near the outer edge while the girl is at the center. Who has the greater tangential acceleration?
Both have zero tangential acceleration
A uniform solid SPHERE has mass M and radius R. If these are increased to 2M and 3R, what happens to the sphere's moment of inertia?
By a factor of 18 (mr^2.....(2)(3^2) = 18)
A 3.0-kg object moves to the right at 4.0m/s. It collides head-on with a 6.0-kg object moving to the left at 2.0m/s. Which statement is correct? A) The total momentum both before and after the collision is 24 kg * m/s B) The total momentum before the collision is 24 kg * m/s, and after the collision is 0 kg * m/s C) The total momentum both before and after the collision is zero D) None of the above is true
C
A very heavy object moving with velocity v collides head-on with a very light object moving with a velocity of -v. The collision is elastic, and there is no fraction. The heavy object barely slows down. What is the speed of the light object after the collision? A) nearly v B) nearly 2v C) nearly 3v D) nearly infinite
C
In an inelastic collision, if the momentum is conserved, then which of the following statements is true about kinetic energy? A) Kinetic energy is also conserved. B) Kinetic energy is gained C) Kinetic energy is lost D) none of the above
C
Which of the following is a false statement? A) For a uniform symmetric object, the center of mass is at the center of symmetry. B) For an object on the surface of the Earth, the center of gravity and the center of mass are on the same point. C) The center of mass of an object must lie within the object. D) The center of gravity of an object may be thought of as the "balance point"
C
The point around which an object naturally spins is called its
Center of mass
Two children are riding a merry-go-round. Child A is at a greater distance from the axis than child B. Which child has the larger linear displacement
Child A
Two children are riding on a merry-go-round. Child A greater distance from the axis of rotation then child B. Which child has a larger tangential acceleration?
Child A
Two children are riding on a merry-go-round. Child A is at a greater distance from the axis of rotation the child B which child has the larger 10 tangential speed.
Child A
Two children are riding on a merry-go-round. Child A is that a greater distance from the axis of rotation then child B. Which child has a larger centripetal acceleration?
Child A
A 3.0-kg object moves to the right at 4.0 m/s. It collides in a perfectly inelastic collision with a 6.0 kg object moving to the left at 2.0 m/s. What is the total kinetic energy after the collision? A) 72 B) 36 J C) 24 J D) 0 J
D
A plane, flying horizontally, releases a bomb, which explodes before hitting the ground. Neglecting air resistance, the center of mass of the bomb fragments, just after the explosion A) is zero B) moves horizontally C) moves vertically D) moves along a parabolic path
D
A rubber ball with a speed of 5.0 m/s collides head-on elastically with an identical ball at rest. What is the speed of the initially stopped ball after the collision? A) zero B) 1.0 m/s C) 2.5 m/s D) 5.0 m/s1
D
Consider two unequal masses, M and m. Which of the following statements is false? A) The center of mass lies on the line joining the centers of each mass. B) The center of mass is closer to the larger mass. C) It is possible for the center of mass to lie within one of the the objects? D) If a uniform rod of mass m were to join the two masses, this would not alter the position of the center of mass of the system without the rod present.
D
Is it true that "the total angular momentum of a system of particles changes when a net external force acts on the system"?
Eh only sometimes, cause why should physics ever be a definite science. It depends on the force's point of application.
3) Two small balls, A and B, attract each other gravitationally with a force of magnitude F. If we now double both masses and the separation of the balls, what will now be the magnitude of the attractive force on each one?
F (equal to each other)
20) If the sum of the external forces on an object is zero, then the sum of the external torques on it must also be zero.
False
Where should a force be applied on a lever arm to produce the most torque
Farthest from the axis of rotation
2) When an object moves in uniform circular motion, the direction of its acceleration is
Is directed towards the center of its circular path
The center of mass of an object
Is sometimes outside of the object ex. Donut
An ice skater performs a pirouette (I promise, it's just a fast spin) by pulling in his/her outstretched arms close to his/her body. What happens to his/her moment of inertia about the axis of rotation?
It decreases
An ice skater performs a pirouette (a fast spin) by pulling in his/her outstretched arms close to his/her body. What happens to his/her angular momentum about the axis of rotation?
It don't change fam
A car is moving in a circular path. At a certain instead, it has zero tangent you acceleration and a non-zero centripetal acceleration. What is the car doing at that instant?
It has: nonzero tangency a velocity, nonzero angular velocity, zero angular acceleration
An ice skater performs a pirouette (still a fast spin) by pulling in his/her outstretched arms close to his/her body. What happens to his/her rotational kinetic energy about the axis of rotation?
It increases
The earth moves about the sun in an elliptical orbit - in case you've forgotten that since the last question like thirty seconds ago. What happens to the Earth's speed as it moves closer to the sun?
It increases - but wait I thought you just said it was constant???? Ha yeahhhh welcome to physics, say one thing and you're guaranteed to be wrong a minute later.
The Earth orbits the Sun in an elliptical orbit - in case you've forgotten having gone over that literally every year since birth. Ignoring friction, what happens over time to the earth's angular momentum about the Sun?
It remains constant - if it didn't then each year would slowly get faster or slower and tbh idk which would suck worse.
suppose a ball is thrown straight up. make a statement about the velocity and the acceleration when the ball reaches the highest point.
Its velocity is zero and its acceleration is not zero
When an object is released from rest and falls in the absence of friction, which of the following is true concerning its motion?
None of the above is true
Suppose a solid sphere of mass M and radius R rolls without slipping down an inclined plane starting from rest. The linear velocity of the sphere at the bottom of the incline depends on what?
Psych! It doesn't depend on neither the mass nor the radius of the sphere! What does it depend on? Who knows! Just not those.
Angular displacement is usually expressed in what unit?
Radians
Angular velocity is expressed in units of what?
Radians per Second
Angular acceleration is expressed with what unit?
Radians per Second^Squared
Two equal forces are applied to a door. The first is applied at the midpoint of the door; the second is applied at the knob. Both are perpendicular. Which exerts greater torque?
The Second at the doorknob, hence why there's a knob there...
5) The reason an astronaut in an earth satellite feels weightless is that
The astronaut is falling
A boy and a girl are even still riding on a merry-go-round, which is starting to look more like a vomit-around, that is turning at a constant rate. The boy is near the outer edge trying not to hurl, and the girl is closer to the center because she blacked out and can't move. Who has the greater centripetal acceleration?
The boy does
A boy and a girl are, surprise surprise, riding on a merry-go-round that's turning at a constant rate. The boy is near the outer edge starting to regret his life decisions, and the girl is closer to the center crying because she dropped her phone and it when flying away. Who has the greater linear speed?
The boy does
Two equal forces are applied to a door at the knob. The first is applied perpendicular to the door, the second at a 30 degree angle like a noob. Which exerts more torque?
The first applied perpendicular to the door.
1) When a car goes around a circular curve on a horizontal road at constant speed, what force causes it to follow the circular path?
The friction force from the road
What is the quantity used to measure an objects resistance to changes in motion?
The moment of Inertia
Suppose a solid sphere of mass M and radius R rolls without slipping down an inclined plane starting from rest. The angular velocity of the sphere at the bottom of the incline depends on what?
The radius of the sphere
11) Two forces produce equal torques on a door about the door hinge. The first force is applied at the midpoint of the door; the second force is applied at the doorknob. Both forces are applied perpendicular to the door. Which force has a greater magnitude?
The second at the doorknob
Rolling without slipping depends on what?
The static friction between the rolling object and the surface it is rolling on
A brick is dropped from the top of a building. A second brick is thrown straight down from the same building. They are released at the same time. Neglect air resistance. Compare the accelerations of the two bricks.
The two bricks accelerate at the same rate
Two children are riding on a merry-go-round. Child A is at a greater distance from the axis of rotation then child B. Which child has the larger angular displacement?
They have the same nonzero angular displacement
Two children are riding on a merry-go-round. Child A's at a greater distance from the axis of rotation then child B. Which child has the larger angular speed
They have the same nonzero angular speed
In what circumstances can the angular velocity of a system of particles change without any change in the system's angular momentum?
This can only happen if the forces acting on the system are INTERNAL to the system.
Which of the following quantities measures the ability of a force to rotate or accelerate an object around an axis
Torque
Supposed another doorknob is placed at the center of a door compared with a door whose doorknob is close to the edge what amount of force must be applied to the doro to produce the torque exerted on the other door
Two times as much
If you cannot exert enough force to loosen a bolt with a wrench which of the following should you do
Use a wrench with a longer handle
Short answer #2: An 82-kg painter stands on a long horizontal board 1.55 m from one end. This 27-kg board is uniform, 5.5 m long, and supported at each end by vertical posts. a) What is the magnitude of the total force provided by both posts? b) with what force does the post that is closest to the painter push upward on the board?
a) 1100 N b) 710 N a) Ftotal = Fa+Fb = (82)(9.81) + (27)(9.81) = 1069.27. Use two sig figs --> 1100N b) [delta]T= -(5.5/2)(27)(9.81) - (5.5-1.55)(82)(9.81) + (5.5)(Fa) = (728.4 + 3177)/5.5 = Fa --> 710 N
newtons first law
an object will travel at constant velocity, unless acted upon by an external force
A ball is thrown straight up, reaches a maximum height, and then it falls to its initial height. Make a statement about the direction of the velocity and acceleration as the ball is coming down.
both its velocity and its acceleration point downward
Newtons Law of gravitational force
everything in the universe with mass attracts all other objects with mass
Suppose a ball is thrown straight up. What is its acceleration just before it reaches its highest point?
exactly g
newtons third law
for every action, there is an equal and opposite reaction
4) A satellite encircles Mars at a distance above its surface equal to 3 times the radius of Mars. If gm is the acceleration due to gravity at the surface of Mars, what is the acceleration due to gravity at the location of the satellite?
gm/16
Ball A is dropped from the top of a building. One second later, ball B is dropped from the same building. As time pogresses, the distance between them,
increases
suppose a skydiver jumps from a high-flying plane. What is her acceleration when she reaches terminal velocity?
it is essentially zero
When an object is released from rest and falls in the absence of friction, which of the following is true concerning its motion?
its acceleration is constant
suppose a ball is thrown downward in the absence of air resistance. make a statement concerning its acceleration
its acceleration is constant
Suppose a ball is thrown straight up, reaches a maximum height, and then it falls to its initial hieght. Make a statement about the direction of the velocity and acceleration as the ball is going up.
its velocity points upward and its acceleration points downward
Kepler's first law
planets orbit the sun in elliptical orbits with the sun at one focus
Ball A is dropped from the top of a building. One second later, ball B is dropped from the same building. As time progresses, the difference in their speeds
remains constant
If a constant net torque is applied to an object, that object will do what?
rotate with constant angular acceleration
newtons second law
the acceleration of an object is directly proportional to the net force acting on the object and inversely proportional to the mass of the object
Kepler's second law
the imaginary line connecting the sun and a planet sweeps out in equal areas in equal times
Hooke's law
the restoring force is directly proportional to the displacement from equilibrium
Kepler's third law
the square of the period of revolution is proportional to the cube of the distance between the planet and the sun
Two objects are thrown from the top pf a tall building. One is thrown up, and the other is thrown down, both with the same initial speed. What are their speeds when they hit the street?
they are traveling at the same speed
