Phys 1010 Midterm

A swimmer bounces straight up from a diving board and falls feet first into a pool. She starts with a positive vertical velocity of 4.00 m/s, and her takeoff point is 1.80 m above the pool. How long is she in the air (in seconds)?

0.816

Suppose you add two vectors A and B . What relative direction between them produces the resultant with the greatest magnitude? What is the maximum magnitude?

0^0, A+B

A 20.0-m tall hollow aluminum flagpole is equivalent in strength to a solid cylinder 4.00 cm in diameter. A strong wind bends the pole much as a horizontal force of 900 N exerted at the top would. How far to the side does the top of the pole flex? The Shear Modulus of aluminum is 2.5 x 1010 N/m2.

0.57 mm

Calculate the acceleration of a skier heading down a 10.00 slope, assuming the coefficient of kinetic friction for waxed wood on wet snow is 0.10. You can neglect air resistance. Hints: HW problem 5.9 may help you. You do not need the mass of the skier.

0.737 m/s2

The force applied in shear deformation is:

Parallel to the surface area, A.

Which is true of significant figures?

When multiplying or dividing measured values, final answer cannot contain more significant figures than the least precise value

Using approximate values, calculate the slope of the curve in Figure 2.62

0.24 m/s

A seagull flies at a velocity of 9.00 m/s straight into the wind. If it takes the bird 20.0 min to travel 6.00 km relative to the Earth, what is the velocity of the wind?

-4.00 m/s

There is a 250-m-high cliff at Half Dome in Yosemite National Park in California. Suppose a boulder breaks loose from the top of this cliff. With what velocity will it strike the ground, assuming that we define the ground to be a height of 0 meters?

-70 m/s

The speed of propagation of the action potential (an electrical signal) in a nerve cell depends (inversely) on the diameter of the axon (nerve fiber). If the nerve cell connecting the spinal cord to your feet is 1.1 m long, and the nerve impulse speed is 18 m/s, how long (in seconds) does it take for the nerve signal to travel this distance?

0.061 s

Suppose two children push horizontally, but in exactly opposite directions, on a third child in a wagon. The first child exerts a force of -75.0 N, the second a force of +90.0 N, friction is -12.0 N, and the mass of the third child plus wagon is 23.0 kg. What is the acceleration?

0.130 m/s^2

Two children pull a third child on a snow saucer sled exerting forces and as shown in Figure 4.36. Find the magnitude of acceleration of the 49.00-kg sled and child system. Note that the direction of the frictional force is unspecified; it will be in the opposite direction of the sum of and .

0.14 m/s2

Determine the coefficient of kinetic friction between two objects in the angle of incline is 15o.

0.27

Match the definitions: __3__ approximation __2__ units __4__ accuracy __5__ conversion factor __1__ uncertainty __6__ precision __7__ significant figures

1. a quantitative measure of how much your measured values deviate from a standard 2. a standard used for expressing and comparing measurements 3. an estimated value based on prior experience and reasoning 4. the degree to which a measured value agrees with correct value for that measurement 5. a ratio expressing how many of one unit are equal to another unit 6. the degree to which repeated measurements agree with each other 7. express the precision of a measuring tool used to measure a value

Match the symbol with the appropriate term: __8__ f __1__ N __7__ g __5__ T __2__ N __3__ F __6__ w __4__ m

1. normal 2. Newton 3. force 4. mass 5. thrust 6. weight 7. gravity 8. friction

Find the following for path B in Figure 3.54: the total distance traveled, and the magnitude and direction of the displacement from start to finish. The various lines represent paths taken by different people walking in a city. All blocks are 120 m on a side.

1.20 km and 379 m, 71.6o North of East

Tectonic plates are large segments of the Earth's crust that move slowly. Suppose that one such plate has an average speed of 4.0 cm/year. What distance does it move in 1 s at this speed? What is its speed in kilometers per million years?

1.3 x 10^-9 m and 40 km/My

A busy chipmunk runs back and forth along a straight line of acorns that has been set out between his burrow and a nearby tree. At some instant the chipmunk moves with a velocity of -1.15 m/s. Then, 2.11 s later, it moves at a velocity of 1.63 m/s. What is the chipmunk's average acceleration during the 2.11-s time interval in m/s2?

1.32

A person is pushing a box. The net external force on the 60-kg box is stated to be 90 N. If the force of friction opposing the motion is 30 N, what is the acceleration of the box?

1.5 m/s^2

What fraction of Earth's diameter is the greatest ocean depth and the greatest mountain height?

1/1000

Tidal friction is slowing the rotation of the Earth. As a result, the orbit of the Moon is increasing in radius at a rate of approximately 4 cm/year. Assuming this to be a constant rate, to one significant figure, how many million years will pass before the radius of the Moon's orbit increases by 3.84×106 m (1%)?

100 My

During strenuous exercise it is possible to exert forces to the joints that are easily ten times greater than the weight being supported. What is the maximum force of friction in the knee joint of a person who supports 66.0 kg of her mass on that knee under such conditions?

100 N

When rebuilding a car's engine, a mechanic must exert 300 N of force to insert a dry steel piston into a steel cylinder. What is the magnitude of the normal force between the piston and cylinder? Assume the piston is already moving when the mechanic exerts this force. (See table 5.1 for coefficients)

1000 N

A 60-kg skydiver jumps from a height of 6000 m above the ground, falling head-first (pike position). The area of the diver is 0.14 m2. The value for C is 1.0, and the density of air is 1.21 kg/m3. Determine the terminal velocity.

102 m/s

A 90-kg skydiver jumps from a height of 6000 m above the ground, falling head-first (pike position). The area of the diver is 0.14 m2. The value for C is 1.0, and the density of air is 1.21 kg/m3. Determine the terminal velocity.

102 m/s

Calculate the approximate number of atoms in a bacterium. Assume that the average mass of an atom in the bacterium is ten times the mass of a hydrogen atom. (Hint: The mass of a hydrogen atom is on the order of 10−27 kg and the mass of a bacterium is on the order of 10−15 kg.)

10^11

The sides of a small rectangular box are measured to be 1.80±0.01 cm, 2.05±0.02 cm, and 3.1±0.1 cm long. Calculate its volume and uncertainty in cubic centimeters. (Hint: calculate the relative uncertainties for each side of the box - see practice problem)

11±1 cm^3

A 6.0-kg cat pounces with an acceleration of 2.0 m/s2 . What is the net external force on him?

12.0 N

Two children pull a third child on a snow saucer sled exerting forces and as shown in Figure 4.36. Find the direction of acceleration of the 49.00-kg sled and child system. Note that the direction of the frictional force is unspecified; it will be in the opposite direction of the sum of and .

12.4

What force is exerted on the tooth in Figure 4.38 if the tension in the wire is 25.0 N? Note that the force applied to the tooth is smaller than the tension in the wire, but this is necessitated by practical considerations of how force can be applied in the mouth.

12.9 N

A person is pushing a box. The net external force on the 60-kg box is stated to be 90 N. If the force of friction opposing the motion is 30 N, what force is the person exerting on the box?

120 N

The speed of sound in air is measured to be 345 m/s on a certain day. What is this in km/h?

1240 km/h

An Olympic runner competing in a long distance event finishes with a time of 2 hours, 55 minutes, and 41 seconds. The event has a distance of 25.7 miles. What is the average speed of the runner in km/h?

14.1

A bicycle racer sprints at the end of a race to clinch a victory. The racer has an initial velocity of 11.5 m/s and accelerates at the rate of 0.500 m/s2 for 7.00 s. What is the racer's final velocity in m/s?

15.0

A swan on a lake gets airborne by flapping its wings and running on top of the water. If the swan must reach a velocity of 6.00 m/s to take off and it accelerates from rest at an average rate of 0.350 m/s2, How long does this take (in seconds)?

17.1

A 76.0-kg person is being pulled away from a burning building as shown in Figure 4.41. Calculate the tension in T2if the person is momentarily motionless.

194 N

When starting a foot race, a 70.0-kg sprinter exerts an average force of 650 N backward on the ground for 0.800 s. How far does he travel?

2.97 m

A bicycle racer sprints at the end of a race to clinch a victory. The racer has an initial velocity of 10.0 m/s and accelerates at the rate of 0.500 m/s2. If the racer was 300 m from the finish when starting to accelerate, what is the racer's final velocity in m/s?

20

Alcohol consumption slows people's reaction times. In a controlled government test, it takes a certain driver 0.39 s to hit the brakes in a crisis when unimpaired and 1.19 s when drunk. When the car is initially traveling at 93 km / h, how much farther (in meters) does the car travel before coming to a stop when the person is drunk compared to sober?

21

Suppose you first walk 12.0 m in a direction 20owest of north and then 20.0 m in a direction 40.0onorth of east. How far are you from your starting point, and what is the compass direction of a line connecting your starting point to your final position? (If you represent the two legs of the walk as vector displacements A and B , then this problem asks you to find their sum R = A + B . The two displacements A and B add to give a total displacement R having magnitude R and direction in degrees.

26.6 m, 65.1o N of E

Find the north and east components of the displacement for the hikers

3.21 km N and 3.83 km E

A team of eight dogs pulls a sled with waxed wood runners on wet snow (mush!). The dogs have average masses of 19.0 kg, and the loaded sled with its rider has a mass of 210 kg.(a) Calculate the magnitude of the acceleration starting from rest if each dog exerts an average force of 185 N backward on the snow.

3.29 m/s2

A disk between vertebrae in the spine is subjected to a shearing force of 600 N. Find its shear deformation, taking it to have the shear modulus of 1 x 109 N/m2. The disk is equivalent to a solid cylinder 0.700 cm high and 4.00 cm in diameter.

3.34 x 10^-6 m

An infant's pulse rate is measured to be 130±5 beats/min. What is the percent uncertainty in this measurement?

3.85%

The speed of sound in water is measured to be 1485 m/s. What is this in mph?

3322

Two muscles in the back of the leg pull upward on the Achilles tendon, as shown in Figure 4.40. (These muscles are called the medial and lateral heads of the gastrocnemius muscle.) Find the magnitude of the total force on the Achilles tendon.

376

You notice a very one-dimensional-thinking snail crawling along one rail of a railroad track. Naturally, you remove it to a safer place. But before you do, you observe it as it moves from position xi = -90.1 cm to position xf = -50.9 cm along the rail, as measured from a point where one rail abuts the next. What is the snail's displacement Δx in centimeters?

39.2

A 200 N force is applied to a 40 kg object. What is the net acceleration?

4.0 m/s^2

Find the magnitudes of velocities vA and vB in Figure 3.57.(Hint: the angle between vBand the x-axis is 72o.) The two velocities vA and vB add to give a total vtot .

4.41 m/s and 5.07 m/s

You gradually apply a force to a 10. kg wood block on a wood table. What amount of force will cause the block to move? The coefficients of static and kinetic friction are 0.5 and 0.3 respectively. The acceleration due to gravity is 9.8 m/s2.

49. N

Two campers in a national park hike from their cabin to the same spot on a lake, each taking a different path, as illustrated in Figure 3.50. The total distance traveled along Path 1 is 7.5 km, and that along Path 2 is 8.2 km. What is the final displacement of each camper?

5.0 km and 5.0 km

Bryan Allen pedaled a human-powered aircraft across the English Channel from the cliffs of Dover to Cap Gris-Nez on June 12, 1979. He flew for 169 min at an average velocity of 3.53 m/s in a direction 45o south of east. Allen encountered a headwind averaging 2.00 m/s almost precisely in the opposite direction of his motion relative to the Earth. What was his average velocity relative to the air?

5.53 m/s, 45o South of East

A swan on a lake gets airborne by flapping its wings and running on top of the water. If the swan must reach a velocity of 6.00 m/s to take off and it accelerates from rest at an average rate of 0.350 m/s2, how far (in meters) will it travel before becoming airborne?

51.43

A graph of velocity versus time is shown for a world-class track sprinter in a 100-m race (Figure 2.67). How long (in seconds) did it take for her to run the first 50 meters?

6.2 s

A 5.00 x 105 kg rocket is accelerating straight up. Its engines produce 1.250 x 107 N of thrust, and air resistance is 4.50 x 106 N. What is the rocket's acceleration?

6.20 m/s^2

Suppose a 60.0-kg gymnast climbs a rope. What is the tension in the rope (in Newtons) if he accelerates upward at a rate of 1.50 m/s2?

678

Suppose a 60.0-kg gymnast climbs a rope. What is the tension in the rope (in Newtons) if he climbs at a constant speed?

678

Find the following for path A in Figure 2-59: (a) The distance traveled. (b) The magnitude of the displacement from start to finish. (c) The displacement from start to finish. Figure 2-59

7 m, 7 m, 7 m

When starting a foot race, a 70.0-kg sprinter exerts an average force of 650 N backward on the ground for 0.800 s. What is his final speed?

7.43 m/s

What is the area of a circle 3.102 cm in diameter? (note: the units will be cm2, you only need to enter the number)

7.557

Find the following for path D in Figure 2-59: (a) The distance traveled. (b) The magnitude of the displacement from start to finish. (c) The displacement from start to finish. . Figure 2-59

8 m, 4 m, -4 m

Find the north component of the displacement from San Francisco to Sacramento

87

To maintain a constant speed, the force provided by a car's engine must equal the drag force plus the force of friction of the road. What is the drag force for a vehicle at 100 km/h for with a drag area of 0.70 m2? Assume the density of air is 1.21 kg/m3. C is 0.28.

92. N

Question 31 / 1 point Suppose you throw a rock nearly straight up at a coconut in a palm tree, and the rock misses on the way up but hits the coconut on the way down. Neglecting air resistance, how does the speed of the rock when it hits the coconut on the way down compare with what it would have been if it had hit the coconut on the way up?

Same

If you divide the total distance traveled on a car trip (as determined by the odometer) by the time for the trip, are you calculating the average speed or the magnitude of the average velocity? Under what circumstances are these two quantities the same?

Average speed. They would be the same if motion was all along a straight line in the same direction.

A weather forecast states that the temperature is predicted to be −5oC the following day. Is this temperature a vector or a scalar quantity?

Scalar

Which best describes the relationship between displacement and distance traveled?

Displacement is a vector quantity describing the change in position, and distance traveled is the total length travelled

What determines the validity of a model?

Experimental proof, even under limited situations

If the total displacement of an object is zero, the average speed of the object will be zero.

False

The coefficients of static and kinetic friction are identical for a fixed pair of materials.

False

Which analogy describes accuracy from the text?

GPS readings that are spread out, but are centered on a bull's-eye

A rock is thrown straight up. What is the net external force acting on the rock when it is at the top of its trajectory (ignoring air resistance)?

Gravity

For large objects, if the velocity doubles, the drag force will:

Increase by a factor four.

For large objects, if the drag area increases, the drag force will:

Increase.

The units of stress are:

N/m2

The Law of Inertia is also known as:

Newton's first law

If a subway train is moving to the left (has a negative velocity) and then comes to a stop, what is the direction of its acceleration? Is the acceleration positive or negative?

To the right. Positive.

For projectile motion on level ground assuming negligible air resistance (the initial angle being neither 0o nor 90o): Is the velocity ever zero?

No

Is it possible to add a scalar to a vector?

No

Friction is dependent on which of the following forces:

Normal

The breaking stress required to cause permanent deformation to a material is called:

Tensile strenght

If there is a constant velocity in a situation, which statement is true:

The displacement will either increase or decrease linearly

If there is a non-zero constant acceleration, which statement is false:

The displacement will increase or decrease linearly with time

If the acceleration of a system is zero, what can be said about the forces on it?

The forces acting on it must be balanced.

Assuming constant acceleration, what is the relationship between displacement and average velocity on a graph?

There is a linear relationship between displacement and average velocity.

Displacement can be a negative value.

True

Force is a vector due to its mass being a vector quantity

True

If the total displacement of an object is zero, the average velocity of the object will be zero.

True

We will be using models to represent physical concepts in this course.

True

This quantity is the slope of the displacement versus time graph.

Velocity

Can a system have a non-zero velocity while the external force on the object is zero?

Yes

For projectile motion on level ground assuming negligible air resistance (the initial angle being neither 0o nor 90o): Can the speed ever be the same as the initial speed at a time other than at t = 0 ?

Yes, at its maximum height

If someone is riding in the back of a pickup truck and throws a softball straight backward, is it possible for the ball to fall straight down as viewed by a person standing at the side of the road? Under what condition would this occur?

Yes, if the horizontal velocity of the ball is exactly opposite of the horizontal velocity of the truck

If an object is thrown straight up and air resistance is negligible, then its speed when it returns to the starting point is the same as when it was released. Is this true for its velocity?

Yes. The velocity will be the same, since the speed is the same.

Stress and strain are related by:

Young's Modulus

Which of the following are fundamental SI units?

meter kilogram Ampere

Rank the SI prefixes from smallest to largest:

nano micro mili centi kilo giga tera

Which of the following is a vector:

the acceleration of gravity

Identify the time or times ( ta , tb , tc , etc.) in Figure 2.57 at which the acceleration is negative. ta refers to point a on the graph.Figure 2.57

ti, tj, tk, tl

Five galaxies on a straight line, showing their distances and velocities relative to the Milky Way (MW) Galaxy. The distances are in millions of light years (Mly), where a light year is the distance light travels in one year. The velocities are nearly proportional to the distances. The sizes of the galaxies are greatly exaggerated; an average galaxy is about 0.1 Mly across. The great astronomer Edwin Hubble discovered that all distant galaxies are receding from our Milky Way Galaxy with velocities proportional to their distances. It appears to an observer on the Earth that we are at the center of an expanding universe. Figure 3.64 illustrates this for five galaxies lying along a straight line, with the Milky Way Galaxy at the center. Using the data from the figure, calculate the velocities relative to galaxy 2. Identify the statement below that is incorrect. The results mean that observers on all galaxies will see th

vgalaxy 3' = 4400 km/s