PHY111 MC

In the figure, four point masses are placed as shown. Assume that all the numbers in the figure are accurate to two significant figures. What is the y coordinates of the center of mass (or center of gravity of this arrangement?

((8x3)+(2x0)+(4x5)+(6x2))/(8+2+4+6)= 2.8 m

In a police ballistics test, 2.00 g bullet traveling at 700 m/s suddenly hits and becomes embedded in a stationary 5.00 kg wood block. What is the speed of the block immediately after the bullet has stopped moving relative to the block, ignoring friction

(.002* 700)/(5+.002)= 0.28 m/s

A 0.140 kg baseball is thrown with a velocity of 27.1 m/s. It is struck by the bat with an average force of 5000 N, which results in a velocity of 37.0 m/s in the opposite direction from the original velocity. How long were the bat and ball in contact?

(.14 kg(37+27))/5000=1.79 x 10^-3 s

Two air track carts move along an air track towards each other. Cart A has a mass of 450 g and moves toward the right with a speed of 0.850 m/s. Cart B has a mass of 300 g and moves toward the left with a speed of 1.12 m/s. What is the total momentum of the two-cart system?

(.45*.85)-(.3*1.12)= 0.0465 toward the right

It requires 0.30 kJ of work to fully drive a stake into the ground. If the average resistive force on the stake by the ground is 828 N, how long is the stake?

(0.30x10^3)/828= 0.362 m

An apple crate with a weight of 225 N accelerates along a frictionless surface as the crate is pulled with a force of 14.5 N as shown in the drawing. What is the horizontal acceleration of the crate?

(14.5cos19)/(225/9.8)= 0.597 m/s^2

A block is on a frictionless table, on earth. The block accelerates at 3.0 m/s^2 when a 20 N horizontal force is applied to it. The block and table are next set up on the moon where the acceleration due to gravity is 1.62 m/s^2. The weight of the block on the moon is closest to

(20/3)1.62= 11 N

A space station is designed in the shape of a large, hollow donut that is uniformly rotating. The outer radius of the station is 350 m. With what period must the station rotate so that a person sitting on the outer wall experiences "artificial gravity" i.e. an acceleration of 9.8 m/s^2?

(2pi350)/(sqrt[9.8]*350)= 37.5 s

Two forces act on a 4.5 kg block resting on a frictionless surface as shown. What is the magnitude of the horizontal acceleration of the block?

(3.7+5.9cos43)/4.5

A satellite is placed in a circular orbit to observe the surface of Mars from an altitude of 144 km. The equatorial radius of Mars is 3397 km. If the speed of the satellite is 3480 m/s, what is the magnitude of the centripetal acceleration of the satellite?

(3480^2)/((144+3397)(1000))=3.42 m/s^2

The kinetic energy of a car is 8x10^6 J as it travels along a horizontal road. How much power is required to stop the car in 10s?

(8x10^6)/10=8x10^5

At time t=0s an object is observed at x= 0m; and its position along the x axis follows this expression: x=-4t + t^2, where the units for distance and time are meters and seconds, respectively. What is the object's displacement delta x between 1s and 3 s

0 m

Write out the number 8.42 × 10^-5 in full with a decimal point and correct number of zeros.

0.0000842

In the produce section of a supermarket, five pears are placed on a spring scale. The placement of the pears stretches the spring and causes the dial to move from 0 to a reading of 2.0 kg. IF the spring constant is 450 N/m, what is the displacement of the spring due to the weight of the pears?

0.044 m

What is the magnitude of the momentum of a 0.140 kg baseball traveling at 45.0 m/s

0.14*45=6.3 kg m/s

A ball attached to a string starts at rest and undergoes a constant angular acceleration as it travels in a horizontal circle of radius 0.30 m. After 0.65 sec, the angular speed of the ball is 9.7 rad/s. What is the tangential acceleration of the ball?

0.30(9.7)/0.65=4.47 m/s^2

A juggler demonstrates his abilities by keeping a 2.3 kg pipe wrench, a 1.5 kg hatcher, and a 1 kg hammer flying through the air above his head. The white circles on the graph represent the positions of the center of mass of each of the flying object at one instant. What is the x coordinate of the center of mass for the system of these three objects?

0.46 m

An airplane needs to reach a forward velocity of 203.0 km/h to take off. On a 2000 m runway, what is the minimum uniform acceleration necessary for the plane to take flight if it starts from rest?

0.79 m/s^2

When a force of 19 N is applied to a spring, it elongates 0.085 m. Determine the period of oscillation of a 4.0 kg object suspended from this spring.

0.8 s

What is 0.674/0.74 expressed to the correct number of significant figures?

0.91

A quarterback throws a pass at an angle of 35 degrees above the horizontal with an initial speed of 25 m/s. The ball is caught by the receiver 2.55 seconds later. Determine the distance the ball was thrown.

52 m

A bus leaves New York City, takes a non-direct route and arrives in St. Louis, Missouri 23 hours 16 minutes later. If the distance between the two cities is 1250 km, what is the magnitude of the bus' average velocity?

53.7 km/h

What must be your average speed in order to travel 350 km in 5.15 h?

68.0 km/h

A 71 kg man stands on a bathroom scale in an elevator. What does the scale read if the elevator is ascending with an acceleration of 3.0 m/s^2

71(9.8+3)=910 N

When rolled down a mountainside at 7.0 m/s, the horizontal component of its velocity vector was 1.8 m/s. What was the angle of the mountain surface above the horizontal?

75 degrees

Use the work-energy theorem to find the force required to accelerate an electron (m= 9.11 x10^-31 kg) moving along the x axis from 4x10^6 m/s to 1.6x10^7 m/s in a distance of 0.0125 m.

8.75x10^-15 N

A motorist travels for 3.0 h at 80 km/h and 2.0 h at 100 km/h. What is her average speed for the trip?

88 km/h

The velocity of a frog is 8 m/s at 20 degrees above the horizontal. What are the horizontal Vx and Vy components of the frog's velocity

8cos20=7.5 m/s 8sin20=2.7 m/s

A block is dropped from a high tower and is falling freely under the influence of gravity. Which one of the following statements is true concerning this situation? Neglect air resistance.

The kinetic energy increases by equal amounts over equal distances.

An object is moving with constant non-zero velocity. Which of the following statements about it must be true?

The net force on the object is zero

How much kinetic energy does a 0.30 kg stone have if it is thrown at 44 m/s

(.5)(.3)(44^2)= 290.4 J

A warehouse worker uses a forklift to raise a crate of pickles on a platform to a height of 2.75 m above the floor. The combined mass of the platform and the crate is 207 kg. If the power expended by the forklift is 1440 W, how long does it take to lift the crate?

(207(9.8)2.75)/1440= 3.87 s

Maria is at a position x=23 m. She then undergoes a displacement delta x= -50 m. What is her final position?

-27 m

A wrench is used to tighten a nut as shown in the figure. A 12-N force is applied 7.0 cm from the axis of rotation. What is the magnitude of the torque due to the applied force?

.84 N* m

When a fan is turned off, its angular speed decreases from 10 rad/s to 6.3 rad/s in 5.0s. What is the magnitude of the average angular acceleration of the fan?

0.74 rad/s^2

What is sqrt[(4.302(15.6-1.2))/(22.1+19.4)] expressed to the correct number of significant figures?

1.22

A fisherman fishing from a pier observes that the float on his line bobs up and down, taking 2.4 s to move from its highest point to its lowest point. He also estimates that the distance between adjacent wave crests is 48 m. What is the speed of the waves going past the pier?

10 m/s

The components of vectors A and B are given as follows: Ax= 7.6 Ay=-9.2 Bx=-5.1 By=-6.8

13

An eagle is flying due east at 8.9 m/s carrying a gopher in its talons. The gopher manages to break free at height of 12 m. What is the magnitude of the gopher's velocity as it reaches the ground? Note: effects of air resistance are not included in this calculation.

18 m/s

A boy jumps with a velocity of magnitude 20.0 m/s at an angle of 25 degrees above the horizontal. What is the horizontal component of the boy's velocity?

18.1 m/s

The sum of 2 vectors of fixed magnitudes has its minimum magnitude when the angle between these vectors is

180 degrees

Consider four point masses located as shown in the sketch. The acceleration due to gravity is the same everywhere. What is the x coordinate of the center of gravity for this system?

3.0 m

The centers of a 13 kg lead ball and 70 g lead ball are separated by 0.14 m. What is the gravitational force between them?

3.1x10^-9 N

A ball is thrown straight upward from ground level with a speed of 18 m/s. How much time passes before the ball strikes the ground if we disregard air resistance?

3.7 s

A car travels along a highway with a velocity of 24 m/s west. The car exits the highway, and 4 s later, its instantaneous velocity is 16 m/s, 45 degrees north of west. What is the magnitude of the average acceleration of the car during the 4 second interval?

4.5 m/s^2

A projectile is fired at an angle of 55 degrees above the horizontal with an initial speed of 35 m/s. What is the magnitude of the horizontal component of the projectile's displacement at the end of 2 s? How long does it take the projectile to reach the highest point in its trajectory?

40 m 2.9 s

The number of significant figures is 10001

5

What is the sum of 2.67+1.976+2.1 expressed to the correct number of significant figures?

6.7

A 60 kg swimmer suddenly dives horizontally from a 150 kg raft with a speed of 1.5 m/s. The raft is initially at rest. What is the speed of the raft immediately after the diver jumps if the water has negligible effect on the raft?

60(1.5)/150= 0.60 m/s west

The tank of a certain car holds 16 gallons of gasoline. How many liters of gasoline does this tank hold?

61 L

Seven seconds after a brilliant flash of lightning, thunder shakes the house. Approximately how far was the lightning strike from the house?

About 2 km away

The intensity of the waves from a point source at a distance d from the source is I. What is the intensity at a distance 2d from the source?

I/4

Which one has larger kinetic energy: a 500-kg object moving at 40 m/s or a 1000-kg object moving at 20 m/s?

The 500 kg object

Which one of the following statements is true concerning an object executing simple harmonic motion?

The object's velocity is zero when its acceleration is a maximum

Two identical satellites have different circular orbits shown. Which has a higher speed?

The one in the smaller orbit

a pilot drops a package from a plane flying horizontally at a constant speed. Neglecting air resistance, when the package hits the ground the horizontal location of the plane will

be directly over the package

For general projectile motion with no air resistance, the horizontal component of a projectile's acceleration

is always zero

Which of the following quantities are units of impulse?

kg m/s N*s

A frog is resting on a sloped tree branch, as shown in the picture below. The frog has a weight of 15 N. What can you say about the magnitude of the normal force acting on the frog?

n < 15 N

A certain string just breaks when it is under 25 N of tension. A boy uses this string to whirl a 0.75 kg stone in a horizontal circle of radius 2 m. The boy continuously increases the speed of the stone. At approximately what speed will the string break?

sqrt[(25(2))/.75]= 8.16 m/s

A roller coaster starts from rest at the top of an 18 m hill as shown. The car travels to the bottom of the hill and continues up the next hill that is 10 m high. How fast is the car moving at the top of the 10 m hill, if friction is ignored?

sqrt[2(9.8)(18-10)]= 12.52 m/s

If you run a complete loop around an outdoor track (400 m), in 100 s, your average velocity is? average speed?

velocity= 0 speed=4 m/s

The fan blade is slowing down. What are the signs of w and a?

w is negative and a is positive

A projectile fired from a gun has initial horizontal and vertical components of velocity equal to 30 m/s and 40 m/s, respectively. Determine the initial speed of the projectile.

50 m/s

Which requires more work, increasing a car's speed from 0 to 30 mph or from 50 to 60 mph?

50 to 60 mph

A velocity vector has components 36 m/s westward and 22 m/s northward. What are the magnitude and direction of this vector

42 m/s

If, in the figure, you start from the bakery, travel to the cafe, and then to the art gallery? what distance have you travelled? what is your displacement

10.5 km -2.5 km

A train travels at a constant speed of 60.4 miles per hour for 101.5 minutes. What distance does the train cover to the correct number of significant figures?

102 mi

A ball is shot straight up from the surface of the earth with an initial speed of 19.6 m/s. Neglect any effects due to air resistance. What is the magnitude of the ball's displacement from the starting point after 1 second has elapsed?

14.7 m

A circular disk of radius 0.015 m rotates with a constant angular speed of 5.0 rev/s. What is the acceleration of a point on the edge of the disk

15 m/s^2

To get to her physics class, Alice walks 0.25 mi to the bus stop. She takes the bus 1.2 mi to the train station. She takes the train 13 mi and walks the remaining 0.17 mi to her class. How far is her commute expressed to the correct number of significant figures?

15 mi

A water rocket can reach a speed of 75 m/s in 0.050 seconds from launch. What is its average acceleration?

1500 m/s^2

In the quotient A/B*C, A has 5 significant figures, B has 2 significant figures, and C has 3 significant figures. How many figures does the quotient have?

2

A ring, as seen from above is pulled on by 3 forces. The ring is not moving. How big is the force F?

2 (15sin)= 30sin

The following conversion equivalents are given: If a deer runs at 4.7 mi/h, its speed, in meters per second, is closest to

2.1 m/s

A rectangular garden measures 15 m long and 13.70 m wide. What is the length of a diagonal from one corner of the garden to the other?

20 m

Maria is at position x=-23m. She then undergoes a displacement delta x= 50 m. What is her final position?

27 m

A ball moves with a constant speed of 4 m/s around a circle of radius 0.25 m. What is the period of the motion?

2pi(0.25)/4= 0.4 s

The column of Trajan, erected in rome in 106-113 A.D. is 125 feet tall. What is its height in centimeters? (2.54 cm = 1 in)

3810 cm

An automotive test driver travels due north in a prototype hybrid vehicle at 30 mi/h for 2 hours. She then reverses her direction and travels due south at 60 mi/h for 1 hour. What is the average speed of the vehicle?

40 mi/h

Which one of the following statements concerning Newton's first law of motion is false?

All objects in motion have net forces acting on them

Two frisky otters slide down frictionless hillsides of the same height but different slopes. The slope of the hill of otter 1 is 30 degrees, while the slope of the hill of otter 2 is 60 degrees. If both start from rest, which otter is moving faster when she reaches the bottom of the hill?

Both otters have the same speed at the bottom.

Two points are located on a rigid wheel that is rotating with decreasing angular velocity about a fixed axis. Point A is located on the rim of the wheel and point B is halfway between the rim and the axis. Which one of the following statements concerning this situation is true?

Both points have the same instantaneous angular velocity.

All three 50 kg blocks are at rest. The tension in rope 2 is:

Equal to the tension in rope 1

A rock is dropped from a high tower and falls freely under the influence of gravity. Which one of the following statements concerning the rock as it falls is true? Neglect the effects of air resistance.

The rock will gain an equal amount of momentum during each second

A rocket explodes into 2 fragments, one 25 times heavier than the other. The magnitude of the momentum change of the lighter fragment is

The same as the momentum change of the heavier fragment

An object of mass 3, initially at rest, explodes breaking into 2 fragments of mass m and 2m, respectively. Which one of the following statements concerning the fragments after the explosion is true?

The smaller fragment will have twice the speed of the larger fragment

An elevator is suspended from a cable. It is moving upward at a steady speed. Which is the correct free body diagram for this situation as shown in the diagram below.

Two half arrows pointing up, one full arrow pointing down

A box with a weight of 100 N is at rest. It is then pulled by a 55 N horizontal force. Does the box move?

Yes

For which objects is the center of mass located outside of the object

a donut

Note the following situations: In which case will the magnitude of the normal force on the block be equal to (Mg + F sin)

case 1 only

An object is moving to the right in a straight line. The net force acting on the object is also directed to the right, but the magnitude of the force is decreasing with time. The object will

continue to move to the right, with its speed increasing with time

In an inelastic collision involving an isolated system, the final total momentum is

exactly the same as the initial momentum

You are in a train traveling on a horizontal track and notice that a piece of luggage starts to slide directly toward the front of the train. From this observation, you can conclude that this train is

slowing down

A 2.0 kg ball moving eastward at 3.0 m/s suddenly collides with and sticks to a 4.0 kg ball moving northward at 2.0 m/s. What is the magnitude of the momentum of this system just after the collision?

sqrt[6^2+8^2]= 10 kg m/s

A nut needs to be tightened with a wrench. Which force shown below will apply the greatest torque to the nut?

the arrow is pointing straight down and is farthest from the center

A ball is thrown horizontally from the top of a tower at the same instant that a stone is dropped vertically. Which object is traveling faster when it hits the level ground belwo if neither of them experiences any air resistance?

the ball

A particle travels along a curved path between two points P and Q as shown. The displacement of the particle does not depend on

the distance traveled from P to Q

"Giddy-up horsey"! A horse pulls on a cart and the cart pulls back on the horse; do these two opposing forces cancel? If you are not careful with the logic, and the physics, you might come to the conclusion that no matter how hard the horse pulls, it can never move the cart. But you know a horse can pull a cart in "real life" so where is the flaw in this reasoning? The action and reaction forces do not cancel each other out because:

they are not acting on the same body

A stalled car is being pushed up a hill by three people, and it is moving at a constant speed. The net force on the car is

zero