Physics - 141 - Richter (All Exams Multiple Choice)

In which of these situations is a car definitely slowing down? Choose an answer for each

1) The car is going north while accelerating south

2) The car has a negative acceleration ax<0

3) The car is going east while accelerating east

1) Yes

2) No

3) No

A car is traveling at some speed when it hits the brakes, traveling some distance and taking some time to do so. If the car’s initial speed had been twice as large instead, by what amount would the distance and time to come to a stop be multiplied?

Distance to Stop: 0.5,1,2,4,8

Time to Stop: 0.5,1,2,4,8

Distance to Stop: 4
Time to Stop: 2

An object has a position given by x(t) = 3+0.2t-0.04t³. What is the velocity of this object as a function of time? Vx(t)

Bonus - acceleration as a function of time

Vx(t) = 0.2 - 0.12t².

Ax(t) = -0.24t.

An object has an acceleration given by ax(t)= 0.4+0.03t² and it was going 2 m/s at t=0.What is the velocity of this object as a function of time?

Vx(t) = 2 + 0.4t + 0.01t³.

What are the correct unit for the 0.03 coefficient with t² term in the acceleration?

ax(t) = 0.4 +0.03t²

m/s^4

You and your friend race from New York City to Los Angeles and back to NYC taking different routes. You win the race. Which of the following statements must be true?

1) You both traveled the same distance

2) You both had the same displacement

3) You bot had the same average velocity

4) You both had the average speed

1)False

2) True

3) True

4) False

A ball is launched upward. The position vs. time graph of its motion after being launched is shown on the left below. On the middle panel, draw the corresponding velocity vs. time graph. Draw the correct acceleration vs. time graph on the right panels.

Look at phone

While an object is in projectile motion ( with upward being positive) with no air resistance….

The horizontal component of its velocity remains constant and the vertical component of its acceleration is equal to -g

A person kicks a soccer ball and it goes 30m down the field. Then they go up to the Moon and kick it again, this time with twice the initial speed. On the Moon g is 1/6 of that on the Earth. How far will the ball go on the Moon?

720m

You are in an elevator that is accelerating upward. How do you determine the magnitude of the normal force acting on you from the elevator floor?

Use newtons 2nd law (F=ma)

A book is placed on a rough board. One end of the board is slowly lifted up, creating an incline with an angle that increases with time, but the book stays in place. As the angle increases which of these statements are true about the forces on the book?

1) The normal force gets smaller

2) The static frictional force gets larger

3) The maximum static frictional force gets larger

4) The down-slope component of the gravitational force get larger

1) True

2) True

3) False

4) True

A dad and his small child are standing on an ice rink. The child pushes on the dad and they move away from each other. Select correct answer

1) The child gets pushed back by the dad with LARGER/SMALLER/EQUAL force.

2) The child ends up moving away with an LARGER/SMALLER/EQUAL speed than the dad.

1) Equal

2) Larger

A 200 N force is pushing on a box that weights 500 N that is on a rough, level surface, with Us = 0.5. The box is not moving. What is the static frictional force on the box?

200 N

Two unequal masses hung over a pulley by a rope

1) The acceleration is g

2) The tension in the rope is less than 2mg

3) The tension in the rope is more than mg

1) False

2) True

3) True

A force of F = (12N)I + (5N)j was applied to an object that underwent a displacement of d = (4m)I-(16m)j. How much work did the force do on the object?

-32 J

12×4 + 5 x -16

A block is sliding down a ramp that has some friction. Evaluate the sign of the work done by each of the three forces acting on the block.

1) The force of friction from the ramp

2) The force of gravity

3) The normal force from the ramp

1) Negative

2) Positive

3) Zero

How long will it take a 7.08hp motor to lift a 250kg beam directly upward at constant velocity from the ground to a height of 45m. Assume frictional forces are negligible.

20.9 s

A vertical spring with spring constant k, initially compressed distance d, launches an object with mass m upward. The object reaches some maximum height h above where it started. If the spring is replaced by a different spring with twice the spring constant and the object is launched in the same way, how high does it go?

2h

The potential energy of a system as a function of position is shown in the graph on the right with several points labeled with letters. Write the appropriate letters with the questions.

1) At which labeled position is the force the largest in magnitude, ????

2) At which labeled positions (s) is the force zero?

3) Which labeled positions is stable equilibrium?

1) C

2) B,D

3) D

A rubber ball and a snowball, both with the same mass, are dropped from the same height onto a force plate that measures the force acting between the object and the plate. The snowball splats, not rebounding upward at all, while the rubber ball rebounds up to about where it fell from. Both impacts take the same amount of time.

1) T or F - The force plate registers a larger force for the rubber ball (larger in magnitude)

2) T or F - The rubber ball experiences a larger change in kinetic energy (larger in magnitude)

3) T or F - The rubber ball experiences a larger change in momentum (larger in magnitude)

1) True

2) False

3) True

Two ice skaters are skating along together when they push off each other. Only one of the following pictures depicts a possible outcome of this “explosion”. Which one is it? The vectors show the momentum of the skaters before and after the explosions.

A

Three point particles with different masses are arranged in a triangle as shown. Where is the center of mass of the system?

X = 0

Y = a/2

Four equal point masses are positioned at the corners of a square. The axis of rotation is different in case.

1) Largest moment of inertia

2) Smallest moment of inertia

1) 3

2) 2

The angular position as a function of time for a particular spinning wheel is given by

theta(t) = bt+ct²+dt^4. What is the angular acceleration, a(t)?

A) 2c+12dt²

B) b+2c+4dt³

C) 24dt

D) 1/2bt²+1/3ct³+1/5dt^5

E) None of the above

A

Alice and Bob are riding on a spinning merry-go-round. Bob’s mass is twice Alice’s. Alice is twice as far from the axle as Bob.

1) T or F, Alice’s angular speed is larger than Bob’s

2) T or F, Alice’s tangential speed is larger than Bob’s

3) T or F, Alice’s centripetal acceleration is larger than Bob’s

1) False

2) True

3) True

Newton’s First Law

Inertia

• an object stays in motion unless acted upon an unbalanced force

• Objects stay at rest unless acted upon an unbalanced force

Newton’s Second Law

F=ma

Newton’s Third Law

For every action, there is an equal and opposite reaction

• Forces always occur in pair

Vector Quantities

acceleration, force, displacement, velocity, momentum

Elastic vs. Inelastic Collisions

Elastic → Momentum conserved, KE conserved

Inelastic → Momentum conserved, KE lost

UNITS

• Position

• Velocity

• Acceleration

• Force

• Work

• Momentum

• KE

• Angular Velocity

• Angular acceleration

• Moment of Inertia

• m

• m/s

• m/s²

• N

• J

• Kg m/s

• J

• rad/s

• rad/s²

• kgm²

Conversions:

g → kg: /1000

cm → m: /100

1 min → 60 seconds

1hour → 60 minutes → 3600 seconds

Inelastic Equation Collision

m1v1+m2v2=(m1+m2)vf

Elastic Equation Collision

𝑚1𝑣1𝑖+𝑚2𝑣2𝑖=𝑚1𝑣1𝑓+𝑚2𝑣2𝑓