Phys 221 Exam 1 Study Guide

(A) Can two force vectors of unequal magnitude sum to zero net force? (B) Can three force vectors of equal magnitude sum to zero net force?

(A) no, (B) yes

A block slides on a track from A to B to C to D. The section from A to B to C is frictionless, but for the section from C to D the coefficient of friction is not zero.Is the block's mechanical (ordered) energy increasing, decreasing, or constant in (a) region AB, (b) region BC, and (c) region CD?

(a) constant (b) constant (c) decreasing *see image on H4*

A cart can move to the right or left along a horizontal track (the positive part of the x axis) as shown in the figure below. Neglect friction. A force is applied to the cart. Choose an appropriate force versus time graph for each statement below. (i) The cart moves toward the right (away from the origin) with constant velocity.(ii) The cart moves toward the right and is speeding up at a steady rate (constant acceleration).(iii) The cart moves toward the left and is speeding up at a steady rate (constant acceleration).(iv) The cart moves toward the right, speeds up and then slows down.

(i) E, (ii) A, (iii) B, (iv) G *Refer to picture on H2*

Consider motion in one dimension. (The sign of the vector quantities is their direction indicator.)An object moves in the positive x-direction with speed 4.6 m/s for 4.1 s. It stops for 2.6 s and then accelerates with acceleration -7 m/s2 for 2.5 s.What is the average velocity of this object in units of m/s?Enter a number with two digits behind the decimal point.

-0.33

Consider motion in one dimension. (The sign of the vector quantities is their direction indicator.) An object moves in the positive x-direction with speed 1.6 m/s for 1.3 s. It stops for 3.5 s and then moves in the negative x direction with speed 3 m/s for 3.1 s. What is the displacement of this object in units of meter?Enter a number with two digits behind the decimal point.

-7.22

A boy holds a 40 N weight at arm's length for 10 s. His arm is 1.5 m above the ground. The work done by the force of the boy on the weight while he is holding it is

0

Two cylindrical artificial bones are made of the same material and length, one with twice the radius as the other. When the two have the same tension force applied, the larger bone stretches by what factor compared to the smaller bone

0.25

Two packages are dropped from an airplane. A parachute can increase the cross sectional area of each packages by a factor of 74. The parachute on package 1 fails to open, and the terminal speed of package 1 is 5.1 m/s. The parachute on package 2 opens. What is the terminal speed of package 2 in m/s? Enter a number with one digit after the decimal point.

0.6

Another scheme to catch the roadrunner has failed and a safe falls from rest from the top of a 30.0 m high cliff toward Wile E. Coyote, who is standing at the base. Wile first notices the safe after it has fallen 15 m. How long does he have to get out of the way?

0.72 s

In how many of the following situations does the car have a westward acceleration? -- The car travels westward at constant speed.-- The car travels eastward and speeds up.-- The car travels westward and slows down.-- The car travels eastward and slows down.-- The car starts from rest and moves toward the east.

1

An apple at rest weighs 1 N. Now assume the same apple is in free fall near the surface of Earth. Neglect friction. The net force on the apple while it is in free fall is

1 N

A car with a mass of 750 kg is moving to the right with a constant acceleration of 1.6 m/s2.What is the total force (in N) on the car?Enter a integer. Round up or down correctly.

1,200

A spring is stretched by 2.6 cm when a force of 2 N is applied. If a force of 3.5 N is applied, how many additional cm does the spring stretch? Enter a number with two digits behind the decimal point.

1.95

As a bacterium swims through water it propels itself with its flagella so as to overcome the frictional drag forces and move at, more or less, constant velocity of 100 micrometer/s for periods of time. If the frictional drag force on a bacterium is 0.1 N, how much work does the bacterium do in 1 s?

10 microJoule

A vector of magnitude 20 is added to a vector of magnitude 25. The magnitude of this sum might be

12

By what factor does the drag force on a car increase as its speed increases from 25 km/h to 100 km/h?

16

A 4.1 kg object is brought to a stop from a speed of 2.3 m/s in 0.1 m by a spring system. What is the spring constant k of the spring? Enter an integer. Round up or down correctly.

2,169

A 90 kg runner with a speed of 5.1 m/s makes a sharp turn with a radius of 1 m to avoid a collision. What is the magnitude of the frictional force (in N) the ground exerts on the runner during the turn? Enter an integer. Round up or down correctly.

2,341

Find the magnitude of the average force (in N) needed to bring a 1,936 kg car to rest from a speed of 71 km/h in a distance of 156 m.Enter an integer. Round up or down correctly.

2,414

A 1,235 kg car starts from rest. A constant force of 257 N acts on it. What is the distance (in m) it travels in 4.9 s? Enter a number with two digits behind the decimal point.

2.5

The mass of atoms is often given in atomic mass units (u). (1 u = 1.66*10-27 kg) The mass of a hydrogen atom is 1 u, the mass of a carbon atom is 12 u, and the mass of a oxygen atom is 16 u. Calculate the mass, in kg, of a water molecule, H2O.

2.99*10-26

An 2.1 kg object gains height 5.2 m while being accelerated from rest to a final speed of 9.8 m/s by an external force. What was the work (in J) done on the object by this force? Let g = 9.8 m/s2. Enter an integer.

208

An ideal spring with a spring constant of 1.6 N/cm and an equilibrium length of 19 cm hangs vertically from the ceiling. A 0.9 kg mass is attached to it. After all motion has damped out, what is the new length of the spring in cm? Enter a number with 1 digit behind the decimal point Let g = 9.8 m/s2..

24.5

Suppose you do 1000 J of work on a 4 kg object, and all the work goes into lifting it above the ground. How high above the ground will the object be when all the work has been done?

25 m

A car engine delivers 3.7 * 104 W to its wheels when moving at a constant speed of 10.4 m/s. What is the magnitude of the resistive force (in N) acting on the automobile at that speed? Enter an integer.

3,558

Consider motion in one dimension. (The sign of the vector quantities is their direction indicator.) An object moves in the positive x-direction with speed 9.2 m/s for 3.9 s. It stops for 3.3 s and then moves in the negative x direction with speed 1.6 m/s for 2 s. What is the average velocity of this object in units of m/s?Enter a number with two digits behind the decimal point.

3.55

The mass of a a satellite in geostationary orbit is 1,361 kg. The mass of Earth is 5.97*1024 kg. Because of the force Earth exerts on the satellite, it accelerates. The magnitude of the acceleration is 0.223 m/s2, and it is directed towards Earth.What is the magnitude of the force in N the satellite exerts on Earth? Enter an integer, Round up or down correctly.

304

A 5 kg object is sliding on a surface with a coefficient of kinetic friction of 0.57. If at t = 0 it has a speed of 24 m/s, at what time (in s) will it come to rest? Let g = 9.8 m/s2. Enter a number with one digit after the decimal point.

4.3

A person walks first at a constant speed of 6 m/s along a straight line from point A to point B and then back along the line from B to A at a constant speed of 4 m/s. What is her average speed over the entire trip?Hint: Assume the distance between A and B is d. How much distance does the person cover on her trip? How long does it take her to cover this distance?

4.8 m/s

A driver in a car accelerating towards the right has an apparent weight with components 997 N pointing down and 496 N pointing towards the left. What is the magnitude of the acceleration of the car in m/s2? Enter a number with 1 digit after the decimal point. Let g = 9.8 m/s2.

4.9

A ball is projected horizontally with speed 21.8 m/s from the top of a 30.1 m high building. Neglecting drag, what is its horizontal distance (in m) from the bottom of the building when it hits the ground? Let g = 9.8 m/s2. Enter a number with 1 digit behind the decimal point.

54

A person weighing 704 N stands in an elevator that decelerates at a rate of 1 m/s2 while moving upward. What is the magnitude of the force in N exerted on the person by the floor of the elevator while it is decelerating? Use g = 9.8 m/s2. Enter an integer. Round up or down correctly.

632

An object's velocity in the positive x-direction changes from 1.4 m/s to 9.1 m/s in 3.5 s.A force of constant magnitude 18 N is acting on it. What is the object's mass in kg? Enter a number with two digits behind the decimal point.

8.18

Consider motion in one dimension. (The sign of the vector quantities is their direction indicator.) An object moves in the positive x-direction with speed 1.5 m/s for 3.8 s. It stops for 1.8 s and then moves in the negative x direction with speed 1.6 m/s for 1.7 s.What is the total distance traveled by the object in units of meter?Enter a number with two digits behind the decimal point.

8.42

A person weighing 766 N stands in an elevator that decelerates at a rate of 1.4 m/s2 while moving downward. What is the magnitude of the force in N exerted on the person by the floor of the elevator while it is decelerating? Use g = 9.8 m/s2. Enter an integer. Round up or down correctly.

875

An 5.3 kg object gains height 9.8 while being accelerated from rest to a final speed of 5.9 m/s by an external force. What was the net work (in J) done on the object? Let g = 9.8 m/s2. Enter an integer.

92

How much work (in J) must a person do to lift 3 bundles of shingles each weighing 18 pounds 13 feet onto a roof? 1 pound = 4.448 N, 1 foot = 0.305 m Enter an integer. Round up or down correctly.

952

Two pitchers are standing side by side, and simultaneously throw baseballs A and B. The balls follow the parabolic trajectories shown. Which of the following statements is true?

Ball B his the ground before ball A. *Refer to image on A3*

You drop an object from a bridge and simultaneously, you throw a-other object downwards at 10 m/s. As the objects are falling, which object has the larger acceleration? (Ignore air resistance.)

Both objects have the same acceleration.

Car 1 starts from rest along a straight highway with constant acceleration a = 1 m/s2. Car 2 passes car 1 with constant velocity of 120 km/hr. Which car is acted on by a larger net force?

Car 1

A small metal cylinder rests on a circular turntable, rotating at a constant speed, as illustrated in the diagram above. Which of the sets of vectors best describes the velocity, acceleration, and net force acting on the cylinder at the position indicated in the diagram?

D. *Refer to image on A3*

Consider the following five graphs (note the axes carefully). Which of these represent(s) one-dimensional motion at constant acceleration, including a = 0?

I, II, IV and V only. *SEE GRAPHS ON H1*

A clever physics student is able to sneak a scale on a popular ride at an amusement park. Before the ride begins to move, the scale reads 700 N for the student's weight. As the ride lifts, it initially accelerates upward at 3 m/s2. At the top, the riders are held in suspense before the gondola is allowed to free fall downward with acceleration equal to g. What should the scale read for the student's apparent weight during the lift and the fall?

Lift: 910 N, Fall: 0 N

Run the simulation Energy Skate Park Basic (Links to an external site.) and choose Playground. Construct a track as shown, small mass, no friction. You have two choices for the skateboard. It can either run in a groove and be fixed to the track (left choice) or it can be allowed to come off the track (right choice). Start the skater in the position shown with the skateboard allowed to come off the track.

Mechanical energy is conserved. The skater returns to his starting position.

A ball is thrown straight upward. It rises in the air and then falls back to earth. Neglect friction.

On the way up, kinetic energy is converted to potential energy.

Which of the following statements about distance and/or displacement are TRUE? (1) Distance is a vector quantity and displacement is a scalar quantity.(2) If a person walks in a straight line and never changes direction, then the distance and the magnitude of the displacement are exactly the same.(3) The diagram below depicts the path of a person walking from position A to B back to C to and then to D. The distance traveled is 90 yds.(4) For the same diagram below, the displacement of the person walking from A to B to C to D is 50 yds.

Only statements 2 and 3 are true.

Which of the following observations about the frictional force is incorrect?

The magnitude of the force of static friction is always proportional to the normal force.

In an inertial frame, an object cannot remain at rest unless which of the following holds?

The net force acting on it is zero.

A box is at rest on a flat table. Which of the following is true?

The normal force and the gravitational force are equal in magnitude and opposite in direction.

A woman pulls a crate up a rough, inclined plane at constant speed. Which one of the following statements concerning this situation is false?

The work done on the object by gravity is zero.

You are cutting wood with a hand saw. You have to push the saw away from you as it moves away from you and pull it towards you as it moves towards you. When are you doing positive work on the saw?

When pushing it away from you and when pulling it towards you.

Is it possible to have motion in the absence of a net force?

Yes

Can an object's velocity change direction when its acceleration is constant?

Yes, this is possible, and a rock thrown straight up is an example.

In order to do a positive amount of work you must

exert a force and move in the direction of the force.

Your class is rather unhappy with the instructor, and they pitch in and decide to fund a sabbatical for him to go to Mars. Unbeknownst to the students the following semester, the instructor has made long distance course arrangements so the "show can go on". The instructor begins talking about mass, weight and related things. He correctly makes which following statement:

his mass is still essentially unchanged but his weight is less than on earth.

An object is thrown straight up. At the top of its path

the velocity is zero and the acceleration is equal to g pointing down.

Newton's 3rd law is also called the law of action and reaction. The "reaction" force does not cancel the "action" force because

they act on different bodies.

Refer to the diagram below. Blocks I and II, each with a mass of 1 kg, are hung from the ceiling of an elevator by ropes 1 and 2. What is the force exerted by rope 1 on block I when the elevator is travelling upward at a constant speed of 2.0 m/s?

~10 N *Refer to A3*

A mass m is lowered gently onto a vertical spring of length L with spring constant k until it just touches the spring. Let y be the distance the spring is compressed and v be the velocity of the mass. The mass is released from rest. Which of the following is the equation for conservation of energy?

½mv2 + ½ky2 + mg(L - y) = mgL