Physics Exam 1

(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

Sam and George are riding in separate cars on the freeway. The lanes they are driving in are adjacent. We choose our coordinate system so that both are traveling into the positive x-direction. Sam travels at 65 mph and George travels at 72 mph. (a) What is Sam's velocity relative to George? (b) What is George's velocity relative to Sam?

(a) -7 mph, (b) 7 mph

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

A ball is launched up a ramp by a spring as shown in the figure. At the time when the clock starts, the ball is near the bottom of the ramp and rolling up the ramp as shown. It goes to the top and then rolls back down.For the graphs shown below, the horizontal axis represents the time. The vertical axis is unspecified. Select the number of the graph that could correctly represent(i) the x-component of the ball's position, (ii) the x-component of the ball's velocity, (iii) the x-component of the ball's acceleration

(i) 8, (ii) 3, (iii) 2

A toy car is moving on a straight track along the positive x-axis. It stays to the right of the origin. For the situations described below, choose the letter of the correct acceleration vs. time graphs that corresponds to the motion described. (i) The car speeds up at a constant rate, moving away from the origin. (ii) The car slows down at a constant rate, moving away from the origin. (iii) The car moves at a constant speed toward the origin.

(i) B, (ii) D, (iii) E

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

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 3.6 m/s for 3.2 s. It stops for 4.7 s and then accelerates with acceleration -7.6 m/s2 for 2.2 s. What is the average velocity of this object in units of m/s? Enter a number with two digits behind the decimal point.

-0.68

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 3.8 m/s for 1 s. It stops for 1.5 s and then moves in the negative x direction with speed 1.1 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.

.39

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

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?

0.72s

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 7.6 m/s for 2 s. It stops for 4 s and then moves in the negative x direction with speed 1.2 m/s for 4.5 s. What is the average velocity of this object in units of m/s? Enter a number with two digits behind the decimal point.

0.93

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 1.7 m/s2. What is the total force (in N) on the car?

1,275

How much work (in J) must a person do to lift 4 bundles of shingles each weighing 17 pounds 14 feet onto a roof? 1 pound = 4.448 N, 1 foot = 0.305 m

1,292

A car engine delivers 3.7 * 104 W to its wheels when moving at a constant speed of 19.4 m/s. What is the magnitude of the resistive force (in N) acting on the automobile at that speed?

1,907

Two packages are dropped from an airplane. A parachute can increase the cross sectional area of each packages by a factor of 55. The parachute on package 1 fails to open, and the terminal speed of package 1 is 12 m/s. The parachute on package 2 opens. What is the terminal speed of package 2 in m/s?

1.6

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

A Boeing 737 jet plane lands with a speed of 60 m/s (about 135 mi/h) and can decelerate on a wet runway at a maximum rate of 4 m/s2 as it comes to rest. What is the minimum time needed before the plane will come to rest?

15s

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 stone is thrown directly upward with an initial speed of 6.4 m/s from a height of 16 m. What is the speed of the stone in m/s when it hits the ground?

18.83

A 1,207 kg car starts from rest. A constant force of 440 N acts on it. What is the distance (in m) it travels in 3.5 s?

2.23

A 5 kg object is sliding on a surface with a coefficient of kinetic friction of 0.76. If at t = 0 it has a speed of 18 m/s, at what time (in s) will it come to rest? Let g = 9.8 m/s2.

2.4

A stone is thrown directly upward with an initial speed of 7.8 m/s from a height of 10.5 m. After what time interval (in s) does the stone strike the ground? Use g = 9.8 m/s2.

2.46

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

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

When struck by a club, a golf ball initially at rest acquires a speed of 31 m/s. If the ball is in contact with the club for 1.17 ms, what is the magnitude of the average acceleration (in m/s2)?(Type a number with 3 significant figures into the box.)

26,500

An 2.8 kg object gains height 7 m while being accelerated from rest to a final speed of 7.5 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.

271

The mass of a a satellite in geostationary orbit is 1,218 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?

272

An 9 kg object gains height 6.9 while being accelerated from rest to a final speed of 8 m/s by an external force. What was the net work (in J) done on the object?

288

Use g = 10 m/s2. Water descends from the top of a tall hydroelectric dam. Its gravitational potential energy is eventually converted into electric energy. How much gravitational potential energy is released when 1000 kg of water descend 200 m to the generators?

2e6W

A 83 kg runner with a speed of 6.1 m/s makes a sharp turn with a radius of 0.8 m to avoid a collision. What is the magnitude of the frictional force (in N) the ground exerts on the runner during the turn?

3,861

A girl pulling a sled exerts a 20 N force horizontally for 40 s. How much power does she generate while moving the sled 60 m?

30 W

An ideal spring with a spring constant of 1.4 N/cm and an equilibrium length of 26 cm hangs vertically from the ceiling. A 1.5 kg mass is attached to it. After all motion has damped out, what is the new length of the spring in cm?

36.5

A 2.1 kg object is brought to a stop from a speed of 1.2 m/s in 0.09 m by a spring system. What is the spring constant k of the spring?

373

You have watched one too many old cartoons and decide to drive around town with a giant spring that is 4 m long and attached to the front of your car. You decide to help a semi truck that is stuck and try to push them with your car. You take a running start, and when you contact the truck the spring in your car compresses 3 m. During which portion of the compression did you do the most work on the spring?

3rd m

You walk in a given direction for 15 m during the first 4 seconds of a trip and then 25 m during the next 6 seconds. Your average speed is equal to

4 m/s

Find the magnitude of the average force (in N) needed to bring a 1,443 kg car to rest from a speed of 108 km/h in a distance of 151 m.Enter an integer. Round up or down correctly.

4,300

A spring is stretched by 2.7 cm when a force of 2 N is applied. If a force of 5.1 N is applied, how many additional cm does the spring stretch?

4.19

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?

4.8m/s

You operate a 120 W light bulb for 1 hour. How much energy did you use? (1 W = 1 J/s)

432000J

A person weighing 491 N stands in an elevator that decelerates at a rate of 1.1 m/s2while 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?

436

A ball is projected horizontally with speed 23.2 m/s from the top of a 21.2 m high building. Neglecting drag, what is its horizontal distance (in m) from the bottom of the building when it hits the ground?

48.3

Which position versus time graph does NOT represent motion with constant acceleration?

5

A car moving at 9 m/s crashes into a wall and stops in 0.11 s. Calculate the magnitude of the force (in N) the seat belt exerts on a passenger in the car to bring him to a halt. The mass of the passenger is 64 kg. Enter an integer.

5,236

An object's velocity in the positive x-direction changes from 3.6 m/s to 8.5 m/s in 3.9 s.A force of constant magnitude 7 N is acting on it. What is the object's mass in kg?

5.57

Use g = 10 m/s2. A crane lifts a 200 kg object to a height of 20 m in 8 s. What is its power output?

5000 W

A driver in a car accelerating towards the right has an apparent weight with components 735 N pointing down and 484 N pointing towards the left. What is the magnitude of the acceleration of the car in m/s2?

6.5

A 1200 kg car's speed changes from 0 to 20 m/s in 4 s. What is the average powerof the car motor during this time period? Neglect friction.

60 kW

A 1400 kg car accelerates uniformly from rest to 60 mph in 6 s. Find the net force needed to produce this motion. 1 mile = 1609.344 m

6259 N

The magnitude of the force vector with (x, y) components (5 N, 5 N) is

7.1 N

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 1.7 m/s for 1.5 s. It stops for 4.2 s and then moves in the negative x direction with speed 1.4 m/s for 3.7 s. What is the total distance traveled by the object in units of meter? Enter a number with two digits behind the decimal point.

7.73

A person weighing 821 N stands in an elevator that decelerates at a rate of 1.6 m/s2while 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?

955

A particle is moving with constant speed along the circular path shown. Its velocity vector is shown at two different positions. What is the direction of the acceleration when the particle is at point X?

A

Which system is in a state of stable equilibrium?

A marble in the bottom of a spherical bowl

Which of the following statements about vectors and scalars are TRUE?

A vector quantity has a direction and a scalar does not.

Three trajectories labeled A, B, and C are shown below. For which trajectory is the vertical velocity component at launch the greatest?

All three trajectories have the same initial vertical velocity component at launch

A ball is fired by a cannon from the top of a cliff as shown in the figure below. Which of the path would the cannonball most closely follow?

B

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.

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.

A ball is thrown vertically upward, and as it comes down, it is caught at its initial position. Which of the following graphs best represents the velocity of the ball as a function of time?

C

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

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.

A stone is dropped from the roof of a single story building to the surface of the earth.

It speeds up because of an almost constant force of gravity acting upon it.

A car's speed changes from 20 mph to 60 mph. By what factor does its kinetic energy change?

It will increase by a factor of 9.

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: 910N, Fall: 0 N

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.

The positions of two blocks at successive 0.20-second time intervals are represented by the numbered squares in the figure below. The blocks are moving towards the right. Are the blocks accelerating?

Only the upper block is accelerating

A rock is thrown straight up from the surface of the Earth. Which one of the following statements describes the energy transformation of the rock as it rises? Neglect air resistance.

The KE decreases and the PE increases.

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.

A mass M, attached to a piece of string OM, is whirled round over a person's head in a horizontal circle. At the position shown in the diagram below, the string suddenly breaks. In which direction does the mass M move horizontally after the string breaks?

The mass M moves in the direction III

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 10 kg and a 4 kg mass are acted on by the same magnitude net force (which remains constant) for the same period of time. Both masses are at rest before the force is applied. After this time, the 10 kg mass moves with a speed v1 and the 4 kg mass moves with a speed v2. Which of the following is true?

The ratio v1/v2 is equal to 2/5

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

The graph shows the net force acting on an astronaut during a rocket launch into a stable orbit. During which time interval was the acceleration of the rocket the greatest?

U-V

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.

Two objects are traveling around different circular orbits with constant speed. They both have the same centripetal acceleration, but object A is traveling twice as fast as object B. The orbit radius for object A is

four times the orbit for object B.

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.

You paddle in a Kayak across a calm mountain lake. Each time you pull the paddle backward through the water, from the front of the boat to its rear, the water exerts a force on the paddle that is

in the forward direction, towards the front of the boat

In the absence of air resistance, a ball of mass m is tossed upward to reach a height of 20 m. At the 15 m position, 3/4 of the way up, the net force on the ball is

mg

An elevator is being lifted up an elevator shaft at a constant speed by a steel cable as shown in the figure above. All frictional effects are negligible. In this situation, forces on the elevator are such that

the upward force by the cable is equal to the downward force of gravity.

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.

A woman exerts a constant horizontal force on a large box. As a result, the box moves across a horizontal floor at a constant speed v0. If the woman doubles the constant horizontal force that she exerts on the box, and the force resisting the motion of the box does not change, the box then moves

with constantly increasing speed

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

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