Physics 110 Exams 1-3
The acceleration due to gravity on the surface of Planet A is one-sixth what it is on the surface of Planet B, and the radius of the Planet A is one-fourth that of Planet B. The mass of Planet A is what fraction of the mass of Planet B ( mA/mb =)?
1/96
Two billiard balls of masses m1 = m and m2 = 2m undergo a perfectly elastic head-on collision. Th initial speed of m1 was 5.0 m/s to the right and the initial speed of m2 was 4.0 m/s to the left, what will be their speeds v1′ and v2′ and directions after the collision?
1: m1v1 +m2v2 =m1v1′ +m2v2′ =⇒ 5m+2m(−4)=mv1′ +2mv2′ =⇒ −3=v1′ +2v2′ 2: v1 −v2 =v2′ −v1′ =⇒ 5−(−4)=v2′ −v1′, =⇒ v2′ =9+v1′ −3=v1′ +2(9+v1′) =⇒ v1′ =−7m/s, v2′ =9−7= 2m/s
Which of the following point towards the center of the circle in uniform circular motion? A) Acceleration B) Velocity, acceleration, net force. C) Velocity, acceleration D) Velocity, net force E) Acceleration, net force.
Acceleration, net force
A 10000kg truck collides with a 4000kg car. Which of the following statements must be true? a) The truck did not slow down during the collision, but the car did. b) During the collision, the force on the truck is equal to the force on the car. c) During the collision, the force on the truck is greater then the force on the car. d) During the collision, the force on the truck is smaller than the force on the car. e) The car did not slow down during the collision, but the truck did.
During the collision, the force on the truck is equal to the force on the car.
Two objects, with masses m and M, are originally a distance r apart, and the magnitude of the gravitational force on each one is F. If the masses are changed to 2m and 2M, and the distance is changed to 4r, the magnitude of the new gravitational force is?
F/4
In question 14) above, what is the tension FT in the rope?
FT : FT =m1(gsinθ−a) or, FT =m2(μkg+a)
Two objects are dropped from a bridge an interval of 1.0 seconds apart. Neglect air resistance. During the time that both objects continue to fall, their separation A) increases at first, but then stays constant. B) decreases at first, but then stays constant. C) increases. D) decreases. E) stays constant.
Increases
A car of mass m1 = m collides with and sticks to a second car of mass m2 = 3m that is initially at rest. After the collision, the kinetic energy of the system *Use conservation of momentum*
KEf/KEi = 1/4
A truck has six times the mass of a car and is moving with one half the speed of the car. If Kt and Kc refer to the kinetic energies of the truck and the car respectively, it is correct to say that
KEt = (3/2) KEc
In the previous problem, how high does it climb (l =?) the rough incline plane with?
L = kx^2 / 2mg(ukcosθ + sinθ) = 0.62 m
A disk with mass Md = 2.4 kg and radius R = 0.58 meters is spinning counter-clockwise about a vertical axis through its center with an angular velocity of ωd = 14.3 rad/s. A rod of mass Mr = 1.6 kg and length L = 2R meters that is rotating clockwise with angular velocity of ωr = 4.5 rad/s is dropped on the spinning disk and stuck to it (the centers of the disk and the rod coincide). The combined system continues to spin with a common final angular velocity ωf . Calculate the final angular velocity ωf of the combined system. * Use Conservation of angular momentum and Li = Lf *
Li=Lf ⇒ Idωd−Irω=(Id+Ir)ωf ωf=Idωd−Irω/ Id+Ir = 8.52rad/s
Two blocks, A and B, are being pulled to the right along a horizontal surface by a horizontal 100N pull, as shown in the figure. Both of them are moving together at a constant velocity of 2m/s to the right, and both have the same mass. Which diagram below describes the horizontal forces acting on block A? A. A --> 100N B. 100 N <--A--> 100 N C. No horizontal force acts on A D. A --> 50 N E. A --> 100 N --> 100 N
No horizontal force acts on A
In the figure showing an isolated system, determine the character of the collision. The masses of the blocks, and the velocities before and after, are shown. The collision is
Not possible because it violates conservation of momentum "Pbefore" does not equal "Pafter"
In an inelastic collision of two objects which of the following is true. A) Total energy of the system remains constant. B) The total mechanical energy remains constant C) Total momentum of the system is conserved. D) Only A and C are true. E) A, B, and C are all true.
Only A and C are true
Two objects, one of mass m and initial momentum p and another of mass M and momentum P collided and stick together. M > m. During the collision in general, I Change in the momentum of m is equal and opposite of the change in momentum of M. II The force m exert on M is equal and opposite to the force M exerts on m. III The change in kinetic energy of m is equal and opposite to the change in kinetic energy of M
Only I and II are true
A horizontal disk rotates about a perpendicular axis through its center. Point P is midway between the center and the rim of the disk, and point Q is on the rim. If the disk turns with constant angular velocity, which of the following statements about it are true? I) The linear acceleration of Q is twice as great as the linear acceleration of P. II) The angular velocity of Q is twice as great as the angular velocity of P. III) The centripetal acceleration of Q is twice as great as the centripetal acceleration of P. IV) Q is moving twice as fast as P.
Only III an IV
A uniform solid sphere of radius R and a uniform disk of radius R both roll without slipping. If both objects have the same mass and the same kinetic energy, what is the ratio of the CM velocity of the solid sphere to the CM velocity of the disk?
Rolling: ω = vcm , KEsp = KEdi R KEsp = KEdi --> 7/5v^2sp = 3/4 v^2di => vsp/vdi = sqrt(15/14)
Refer to the figure below, which shows four vectors M, N, S and T. Vector S and T as expressed in terms of vectors M and N are given by... A) S = M + N, T = M - N B) S = N - M, T = M + N C) S = M - N, T = M + N D) S = N + M, T = N -M E) S = N + M, T = -M - N
S = M - N, T = M + N
A rock starts completely outside and is gradually lowered into water. As a rock sinks continuously deeper and deeper into water, how does the buoyant force on it vary? (It continued to be lowered after it is completely submerged) A) The buoyant force remains constant. B) The buoyant force steadily decreases. C) The buoyant force first increases and then remains constant. D) The buoyant force keeps increasing steadily. E) Depends on the density of the rock.
The buoyant force first increases and then remains constant
Consider two less-than-desirable options. In the first you are driving 30 mph and crash head-on into an identical car also going 30 mph. In the second option you are driving 30 mph and crash head-on into a stationary brick wall. In neither case does your car bounce off the thing it hits, and the collision time is the same in both cases. Which of these two situations would result in the greatest impact force? A) hitting the other car B) hitting the brick wall C) The force would be the same in both cases. D) We cannot answer this question without more information. E) None of these is true.
The force would be the same in both cases
Which of the following statements are true about an object in two-dimensional projectile motion with no air resistance? A) The speed of the object is constant but its velocity is not constant. B) The speed of the object is zero at its highest point. C) The horizontal acceleration is always zero and the vertical acceleration is always a non-zero con- stant downward. D) The acceleration of the object is zero at its highest point. E) The acceleration of the object is +g when the object is rising and -g when it is falling.
The horizontal acceleration is always zero and the vertical acceleration is always a non-zero con- stant downward.
A constant force acts on a moving object. The object makes a fixed magnitude of displacement in some direction. In general, in what direction is the displacement that will result in the object traveling with the least kinetic energy after the displacement occurs (maximum negative change in KE)? A) Any direction perpendicular to the force B) The same direction as the force C) The opposite direction as the force D) The direction does not matter. E) In a direction perpendicular to the plane of the force and the velocity of the object
The opposite direction as the force
A rocket explodes into two fragments, one 5 times more massive than the other. The magnitude of the momentum change of the lighter fragment compared to the more massive one is A) 5 times B) 15 times C) The same D) 25 times E) None of the above
The same
In general, when a rigid object rotates about a fixed axis, what is true about all the points in the object? A) They all have the same angular speed. B) They all have the same linear speed. C) They all have the same centripetal acceleration. D) They all have the same linear acceleration. E) None of the above.
They all have the same angular speed
Consider the three vectors V1, V2 and V3 shown in the figure below. What is the magnitude VR and the direction θ of the resultant vector VR = V1 + V2 + V3.
VR = sqrt (Vrx^2 + VRY^2)
Which requires more work, increasing a car's speed from 0 mph to 30 mph or from 50 mph to 60 mph?
W2net > W1net
An object of mass m is sliding down an incline at a constant speed. It is initially at a height h above the ground, as shown in the figure below. The coefficient of kinetic friction between the mass and the incline is μk. If the mass continues to slide down the incline at a constant speed, which of the following formulas gives the magnitude of the energy lost due to friction by the time the mass reaches the bottom of the incline?
Wfr = mgh
Ablockofmass10kgispulledup10mbyaforceof100N upaninclineofangleθ=30◦ asshownin the figure below.The coefficient of kinetic friction μk = 0.2. What is the net work done on the block?
Wnet = d (F -mgsinθ - ukmgcosθ) = 340 J
Which of the following is not possible? A) an object has zero velocity but non-zero acceleration B) an object has constant non-zero velocity and changing acceleration C) an object has constant non-zerio acceleration and changing velocity D) an object has velocity directed east and acceleration directed north E) an object has velocity directed east and acceleration directed west
an object has constant non-zero velocity and changing acceleration
A block of mass m sits at rest on a rough inclined ramp that makes an angle θ with the horizontal and coefficient of satic friction μs. What must be true about force of static friction fs on the block? a) fs > mg. b) fs =μsmgcosθ. c) fs =mgsinθ. d) fs = μsmgsinθ. e) fs =mgcosθ.
fs =mgsinθ
Two masses m1 and m2 are attached with a massless string and are arranged as in the figure bellow. m2 is on a horizontal table with coefficient of kinetic friction μk. The acceleration of the two mass system is...
m1: m1gsinθ−FT=m1a m2: FT−μkm2g=m2a m1 sin θ − μk m2 / a=. m+mg
If you want to increase the kinetic energy of a given mass by a factor of 6, by what factor must you increase its momentum?
p = sqrt (2mKE) Increase by factor of sqrt(6)
Car A is traveling at vA and car B at vB. Car A is ∆xAB behind car B when the driver of car A accelerates his car with a uniform forward acceleration of a. How long after car A begins to accelerate does it take car A to overtake car B? Both cars traveled for the same amount of time t by the time when car A surpasses car B. Get t.
t= ((vb-va) - sqrt(vb-va)^2 + 2a∆xAB)) / a
At a certain depth in the ocean, the absolute pressure is P. If you go to twice that depth... A) the gauge pressure will not change. B) the absolute pressure will be less than 2P. C) the absolute pressure will be greater than 2P. D) the absolute pressure will be 2P. E) the gauge pressure will increase but will not double.
the absolute pressure will be less than 2P
Under what condition is average velocity equal to the average of the object's initial and final velocity? A) This can occur only when the velocity is zero. B) This can only occur if there is no acceleration. C) The acceleration must be constantly increasing. D) The acceleration must be constantly decreasing. E) The acceleration is constant.
the acceleration is constant
When you blow some air above a paper strip, the paper rises. This happens because
the air above the paper moves faster and the pressure is lower
A 10-kg piece of aluminum sits at the bottom of a lake, right next to a 10-kg piece of lead, which is much denser than aluminum. Which one has the greater buoyant force on it?
the aluminum
The reason an astronaut in an earth satellite feels weightless is that... A) the astronaut's acceleration is zero. B) this is a physiological effect associated with rotational motion. C) the astronaut is at a point in space where the effects of the moon's gravity and the earth's gravity cancel. D) the astronaut is falling freely. E) the astronaut is beyond the range of the earth's gravity.
the astronaut is falling freely
A merry-go-round spins freely when Diego moves quickly to the center along a radius of the merry-go- round. As he does this, it is true to say that
the moment of inertia of the system decreases and the angular momentum remains the same
If the sum of torques acting on a rigid body add up to zero...
the rigid body could be both accelerating linearly and turning
A car moving at constant acceleration passes two points x1 and x2 separated by a displacement of ∆x12 in t seconds. If the velocity at the second point x2 is v2, what is the acceleration of the car?
v =v1+v2 =⇒ v1=2v −v2,v =∆x12 a= v2-v1/t = 2v2-2v / t
A basketball player throws a ball as shown in the figure below and makes the basket. The ball is thrown with an initial speed of v0 at an angle of θ from a horizontal distance of ∆x. What was the initial speed v0 of the ball?
v0 = sqrt (g/2(∆xtanθ−∆y)) * ∆x / cos θ
A spring with k = 122.0 N/m is at the base of a θ = 37◦ inclined plane. A 2.5 kg object is pressed against the spring, compressing it 0.41 m from its equilibrium position. The object is then released. How fast is the mass moving when it leaves the spring? μk = 0.2 up the incline plane.
v= sqrt ((K/M)x) = 2.86 m/s
A cylinder of moment of inertia 4.0 kg · m2 about its axis initially rotates at 80 rad/s. A constant torque is applied to slow it to 40 rad/s. If the cylinder takes 10 seconds to reach 40 rad/s, what is the magnitude of the applied torque?
α=ωf−ωi, τ=Iα=m·N
A hoop of radius R and mass M is at rest at the top of an incline plane as shown in the figure below. The hoop rolls down without slipping. When it reaches the bottom, what is the angular momentum of the hoop around its center of mass? Ihoop = MR2
ω= gh gives L=Iω=MR2sqrt(gh) =MR sqrt(gh)
A bicycle is initially traveling at a velocity of 8 m/s. It then accelerated uniformly for 5 seconds and the wheels rolled without skidding 34 revolutions. If the diameter of the bicycle wheel is 66 cm, what is the angular acceleration of the bicycle wheel?
∆ω0 =v0/R,θ=34rev=2π×34rad, t= 5s ∆θ=ω0t+1αt2 =⇒ α=2(∆θ−ωot)= 7,40rad/s2
