Physics Exam 2

Two objects of mass 50 kg move along parallel paths separated by 3m. Both objects have equal speeds of 2.0 m/s. What is the magnitude of the total angular momentum of the two-object system about a point that is in the middle of them?

300

Which of the following is true about Uniform Circular Motion? A) Only the tangential acceleration is zero B) Only the centripetal acceleration is zero C)Both the tangential and centripetal accelerations are zero D)Neither tangential nor centripetal accelerations are zero

A

A block is attached to a fixed object, a, by a spring. At the moment shown, the spring is at its natural length. Which of the following must be true? a. ab=0 b. vb=0 c. ab can't equal 0 d. vb can't equal 0

A. ab=0

A normal bullet and a rubber bullet of the same mass are fired at log. Both hit the log with the same initial momentum. The normal bullet lodges itself inside the log, while the rubber bullet bounces off. If the time interval for stopping the normal bullet and reversing the rubber bullet are the same, which one is more likely to knock over the log? Hint: Which one corresponds to a greater average force? a. normal bullet b. rubber c. equally likely

B

You roll a bowling ball across a floor. How do you have to continuously tap it to get it to move in a circle at constant speed? A) In the direction it's rolling B) Perpendicular to the direction it's rolling C) Perpendicular to the direction it's rolling and in the direction it's rolling D) Perpendicular to the direction it's rolling and opposite the direction it's rolling

B) Perpendicular to the direction it's rolling

A constant force ⃗𝐹P= is applied to two identical cylinders that start from rest and (1) rotates about a fixed, low-friction axle, and (2) rolls without slipping on a horizontal surface. After one full revolution, which cylinder has the larger change in (total) kinetic energy? A) Cylinder 1 B) Cylinder 2 C) The change in the total kinetic energy is the same. D) Cannot be determined since 𝑓!,<= is unknown.

C.

Blaster, with a mass of 200 kg, is now sitting in a cage in an elevator that is going down and slowing down. In which direction is Blaster accelerating relative to 1) Blaster in the cage and 2) a person standing on the ground? A)down, down B)down, up C)0, down D)0, up E)up, up

D, 0,up

A 5-kg book slides across a table with an initial kinetic energy of 10 J. If kinetic friction between the table and the book (μk= 0.204) causes the book to stop after 1 m, how much work does the kinetic friction force do on the book? A. -10 B.-5 C. 0 D. 5 Unable to determind

E

You pull on a block as shown, but the block does not slip. If the magnitude FYb of your force is unchanged, but the angle q is increased, how does the magnitude of the friction force from the table on the block change? A. It increases B. It decreases C. It stays the same D. There is not info to tell

It decreases

You are throwing water balloons at a house. You toss each balloon with the same initial speed and launch angle. What effect will taking a step closer to the window have on the balloon's impact speed (𝑣f) at the house? A. no effect on Vf B. Increases Vf C. Decreases Vf D. It depends

It depends

You pull on a block as shown, but the block does slip. If the magnitude FYb of your force is unchanged, but the angle q is increased, how does the magnitude of the friction force from the table on the block change? A. It increases B. It decreases C. It stays the same D. There is not info to tell

It increases

A bowling ball and a golf ball are both purely translating with the same initial (nonzero) momentum. If you exert the same constant force on each (in the opposite direction of the motion), which takes more time to stop? A. bowling ball B. golf ball C. same D. not enough info

It takes the same time

A car makes one lap around a track at constant speed 𝑣𝑜 in a time T. Over the time it takes to go one lap, how do the magnitude of its average velocity and average speed compare? A) magnitude of average velocity > average speed B) magnitude of average velocity < average speed C) magnitude of average velocity = average speed D) we need more information to determine this

Magnitude of average velocity < average sped

An ideal bouncy ball bounces off an ideally rigid surface so that it always reaches the same height on each bounce. Is the ball undergoing SHM?

NO

In general, when an extended object rotates, which type of acceleration is the same for each small piece of which it is made? A. ac=v^2/r B. at=alphaR C. a= vector combination D. none

None

A platform (p)moves upwards as shown. Initially two objects on it are connected by a compressed spring and then released. The final configuration is just when the spring reaches it uncompressed length. The block (b)slides with kinetic friction and the cylinder (c)rolls without slipping. A) Positive work done on the system B) Negative work done on the system C) Positive change in potential energy D) Negative change in potential energy E) None of these

None of these

A car is initially moving south at 45 mph. It turns left onto a street, comes to an intersection, and then turns right. After another left hand turn, the car is back on the original road moving southagain. At the final time, the car is moving south at 20 mph. Which vector best represents the direction of the car's average acceleration during this motion? A. NorthWest B. North C. North East D. South West E. South

North

You push horizontally on a block that is on a cart. Assume the wheels are good enough that the cart rolls perfectly on the floor. The block does not slip across the cart. A. Right B. Left C. =0 D. It depends

Right

How does the magnitude of the static friction force fs,CBbetween the cart and the block relate to FYB, the magnitude of your pushing force? Again, the block does not slip across the cart. A. Static Friction> F B. Static Friction < F C. Static Friction=F

Static Friction< F

If a physical pulley (p) is rotating about an axle with negligible friction with the angular acceleration shown, what must be trueabout the tension forces? A. T1>T2 B. T1=T2 C. T1<T2

T1>T2

A solid spherical ball starts from rest and rolls without slipping down an inclined plane. Which direction is the friction force on the ball? A) up the plane B) down the plane C) none; the friction force is zero

Up the plane

An electron in a magnetic field moves along a circle with a radius of 39.5 m with a speed that follows: v(t)=v0e−bt where b=0.45 s−1 and v0=265 m/s. What is centripetal acceleration?

V(t)^2/R Ac=23.6 m/s^2

For the points at the top, center and bottom of a ball that rolls without slipping on a stationary surface, which relation below is true? Vtop<Vcenter<Vbottom Vtop=Vcenter=Vbottom Vtop>Vcenter>Vbottom

Vtop>Vcenter>Vbottom

Two objects of equal mass collide as shown. If 𝑣1i= 3m/s, 𝑣2i= 4m/sand 𝑣1f= 5m/s, is the collision elastic?

Yes, 3^2+4^2=5^2

When are the momentum and kinetic energy of a system constant? A) When all of the objects in the system undergo an elastic collision .B) When all of the objects in the system undergo a collision in one dimension. C) When all of the objects in the system undergo a perfectly inelastic collision .D)Whenever the system is completely isolated.

a

A motorcyclist is rounding a flat curve at a constant speed 𝑣. She is more likely to slip if she rides along the a. outside edge b. inside edge c. middle of the curve

b. inside edge of the curve

An electron in a magnetic field moves along a circle with a radius of 39.5 m with a speed that follows: v(t)=v0e−bt where b=0.45 s−1 and v0=265 m/s. What is angular acceleration?

dV(t)/R At=-.348 rad

A baby is doing push-ups on a level floor. He has a 7-kg mass and pushes his body from 5 cm above the floor to 20 cm above the floor. The work done on the baby by the normal force of the floor on the baby is: a. greater than zero b. less than zero c. equal to zero

equal to zero

A bowling ball and a golf ball are both purely translating with the same (nonzero) momentum. Which has the larger kinetic energy? A. bowling ball B. golf ball C. same kinetic energy D. not enough info

golf ball

A bowling ball and a golf ball are both purely translating with the same initial (nonzero) momentum. If you exert the same constant force on each (in the opposite direction of the motion), which travels further before stopping? A. bowling ball B. golf ball C. same D. not enough info

golf ball

Beam 1 with block 2 hanging from it is supported as shown. The mass of block 2 is m2=150 kg, θ=55∘, and x=7 m. You choose the lower left end of the beam as the axis of rotation, and you call clockwise the positive torque direction. Calculate the torque due to the weight of block 2 on the block+beam system.

mgxLsintheta =8.429 Nm

A platform (p)moves upwards as shown. Initially two objects on it are connected by a compressed spring and then released. The final configuration is just when the spring reaches its uncompressed length. The block (b)slides with kinetic friction and the cylinder (c)rolls without slipping. A) Positive work done on the system B) Negative work done on the system C) Positive change in potential energy D) Negative change in potential energy E) None of these

negative work done on the system

A block is initially sliding to the right along a horizontal surface with negligible friction at a speed 𝑣i. When it passes the point 𝑥0 a force ⃗𝐹'% acting to the left begins to slow it down and reverses its motion. When the object gets back to the point 𝑥0 it is moving with a speed 𝑣f < 𝑣i. Using the block as the system, from the time from when the block first passes 𝑥0 to when it returns to 𝑥0 the work done by the force ⃗𝐹'% is ____ and the force is _____: a. Positive, nonconservative b. negative, conservative c. zero, conservative d. positive nonconservative e. negative, nonconservative

negative, non conservative

You plan to throw stones by using a sling that you whirl over your head. You will whirl the stone in a horizontal circle with a radius of 1.9 m at a height of 2.4 m above the ground (this is often referred to as a "conical pendulum", which you saw a picture of in the necklace part of the 3-1 studio). You want the stone to hit a target on the ground a distance of 14.3 m in front of you and 1.9 m to the side (note that this number is the same as the radius of the circle). This means that the stone is released a distance 1.9 m to the side of you, but then travels a distance 14.3 m forward. What must be the magnitude of the centripetal acceleration of the stone just before you release it?

sqrt (2*h)/9.81=t distance/time v^2/r centripetal acceleration =219 m/s^2

A vibration platform oscillates up and down with a fixed amplitude of 5.8 cm and a controlled frequency that can be varied. If a small rock of unknown mass is placed on the platform, at what frequency will the rock just begin to leave the surface so that it starts to clatter? *Hint*: You should recall the condition that helps determine when two objects lose contact. UNITS: Frequency has units of Hertz, or 1/s. Enter your answer with units "s^-1".

sqrt (g/2pi^2*amplitude)

An "ideal" spring with spring constant 0.5 N/m is attached to a block with mass 0.8 kg on one end and a vertical wall on the other. The floor has negligible friction, and you give the block a push and then let go. You observe that the block undergoes simple harmonic motion with a maximum speed of 2.5 m/s.

sqrt(k/m) =.7905 rad/s

Blaster is attached to two fixed walls by springs and slides with negligible friction on the table. Both springs remain stretched throughout the motion and have different spring constants. What is the frequency of oscillation of Blaster?

sqrtk1+k2/mb

A puck is sliding around a circular track that is banked at an angle ϕ with respect to the horizontal such that no friction between the puck and the track is required to keep the puck from slipping up or down the track. If the puck is moving at a speed 33.1 m/s and the radius of the track is 425 m, determine ϕ in degrees.

tantheta = v^2/R*g =14.7 degrees

If v is constant, the particle's angular momentum at Position 1 (with respect to the point shown) isA) larger thanB) smaller thanC) the same as

the same as

Suppose you wish to whirl a pail full of water in a vertical circle at a constant speed without spilling any of its contents (even at the top of the circle!). If your arm is 0.65 m long (from shoulder to fist) and the distance from the handle to the surface of the water is 17 cm, what minimum speed is required?

v= sqrt(gr) =2.836 m/s

A block attached to a spring undergoes SHM. The graph shows the velocity of the mass as a function of time. Which of the following expressions is equal to the amplitude of the position of the block? a. vmax b.vmaxw c.vmax/w d. cannot be determined

vmax/w

Blaster, with a mass of 200 kg, is now sitting in a cage in an elevator that is going down and slowing down, with an acceleration of magnitude 2.0 m/s2. Find the magnitude and direction of the force from Blaster on the cage.

-2362N