Physics留学生代做、Java，c++语言代写、代做Python设计

日期：2020-03-16 08:59

Keep This Page Attached to the Exam

Physics 1A Winter 2020 Final Exam Cover Sheet

INSTRUCTIONS:

Right now, as soon as you get this part of the exam:

1. Fill in this cover sheet completely (which you should have). You need to upload this page separately.

2. Write your response to each problem on a separate paper.

3. Count the pages of the exam. There should be 11 pages in total with probelms and questions on page 2 -

9. If you find this is not the case, email me IMMEDIATELY. It is your responsibility to have a complete exam.

Remember:

* You are only allowed to consult your notes, homework, exams and textbook, and you are encouraged to do

so during the exam. Do not try to search for an answer online. Follow all instructions. If you are asked to

start your response in a certain way, you have to follow it. For multiple choice questions, you have to

explain. In general, an answer without an explanation or steps shown will not receive any credit. *

Don’t Cheat!

We automatically report anyone suspected of cheating to Student Judicial Affairs.

I certify by my signature below that I have read the above instructions and that I will abide by the UC Davis Code

of Academic Conduct. This includes

· not copying from anyone else’s exam

· not letting any other student copy from my exam

· not collaborating with anyone

· not consulting any unauthorized resource

· not discussing this exam with any student who has not yet taken it, nor providing any information, written or

oral, that might get to a student who has not yet taken it

Name (Print Clearly):

Last First

Student ID:

Signature:

| | | | page 2

Last Name First Name First three initials of last name

Grade:

1. (5 points) Mary has written an equation describing the torque (τ ) on an object. However, one factor, (?), is

missing from the equation,

τ = pa(?) ,

where p is the magnitude of the momentum of the object, and a is the magnitude of the acceleration of the

object. In order to have the dimensions/units to work out, (?) has to be: (There is only one answer. Show all

your work to explain your answer.)

I. t, the time since t = 0,

II. d, diameter of the object, or

III. v, speed of the object.

2. (5 points) A driver applies the brakes on a car traveling at 60.0 mph, which we will take it as 26.8 m/s. The

car then stops after traveling for 40.0 m under such a constant acceleration. What is its speed when it has

traveled for 20.0 m after applying the brakes?

26.8 m/s v = 0

20.0 m 20.0 m

v = ?

| | | | page 3

Last Name First Name First three initials of last name

Grade:

3. (5 points) Three identical rocks, rock X, rock Y, and rock Z are thrown with the same speed but in different

directions as shown. If the effect from air resistance is negligible, determine if the following statements are

true or false. Explain your choices.

I. They all hit the ground at the same time. True / False

II. They all hit the ground with the same speed. True / False

III. They all hit the ground with the same vertical component of their velocity. True / False

4. (5 points) Two blocks of masses, m and M, sitting one on top of each other are placed on a smooth frictionless

table as shown. However, the surface between m and M is not smooth. In a stunt, a person applies a force

(F~A) on M towards the right such that M is removed from the table while m remains on the table although

being slightly displaced. Draw two separate free body diagrams for m and M. Is the friction between m and

M kinetic or static? Hint: Look at Problem 4 on midterm 1. What is the difference here?

Free body diagram of m Free body diagram of M

Is the friction between m and M kinetic or static? Briefly explain.

| | | | page 4

Last Name First Name First three initials of last name

Grade:

5. (5 points) A person (mass = 70.0 kg) stands on an elevator which is acclerating upwards at 20.0 m/s2

. Draw a

free body diagram for the person and find the apparent weight he is experiencing. Hint: Look at L6.pdf about

apparent weight.

Free body diagram of the person

6. (5 points) A player throws a basketball straight up at 5.0 m/s from 2.0 m above the ground. It only reaches a

highest height of 3.0 m above the ground, indicating there is a presence of air resistance. From the moment

where the basketball leaves the player’s hand to the moment where the basketball is at the maximum height,

state whether the following quantities are negative, positive, or zero. Explain all your choices. “∆” is defined

as final minus initial.

I. ∆KE, the change of kinetic energy of the basketball: negative / positive / zero

II. ∆P EG, the change of potential energy of the basketball and the Earth: negative / positive / zero

III. WNC, the work done by non-conservative forces: negative / positive / zero

IV. WG, the work done by gravitational force: negative / positive / zero

| | | | page 5

Last Name First Name First three initials of last name

Grade:

7. (5 points) A solid disk of mass 10.0 kg and radius 50 cm is spun from rest by two forces (F~A and F~B) shown.

It is fixed at its center (x). (i) Find the net torque on the disk about its center taking the counter-clockwise

direction as positive. (ii) Find the angular acceleration of the disk. You can safely ignore the normal force and

the weight as they have no contribution to the net torque. Hint: Look at Problem 5 on midterm 2. Can you do

the same set of calculations for a solid disk?

8. (5 points) A table tennis ball moving to the North is also spinning such that it deviates to the West shown in the

top view (left). If we go into the table tennis ball’s rest frame, the wind will be flowing towards the ball as shown

on the right. On the figure to the right, (i) indicate the direction of the spin, (ii) draw at least three streamlines

on each side of the ball, and (iii) indicate which side of the ball has a higher/lower pressure. You may either

print this page or just draw your response on a paper.

Top View Top View (ball’s rest frame) Wind direction

Last Name First Name First three initials of last name

Grade:

9. Ball A traveling to the right at 5.0 m/s impacts a group of two identical balls (B and C) which are both initially

at rest (shown on the left). After the collision, all three balls are moving, and their speeds and directions are

shown on the right. All balls have the same mass of 1.0 kg. The +x and +y directions are defined for you.

a. (6 points) In terms of the quantities given, write down two momentum conservation equations; one for the

x-component and one for the y-component of the balls’ momenta.

b. (4 points) How many independent unknowns are there in part (a)? What are they? They should be very

obvious!

c. (6 points) Solve for the unknowns in part (a).

d. (4 points) Is the collision elastic? Justify your answer by calculating the total kinetic energy before and after

the collision.

| | | | page 7

Last Name First Name First three initials of last name

Grade:

10. These questions test your general understanding of the entire course.

a. (6 points) State three (and only three) distinctively different conservation laws you learned this quarter.

First state the of the conservation laws in words, then present it in a form of an equation (before) = (after).

Finally, write down the condition that needs to be satisfied for the quantity to be conserved.

Example:

xxx is conserved

xxxbef ore = xxxaf ter

This is true when ...

b. (8 points) What are the three important elements of the Newton’s Third Law? Draw two free body diagrams

of the same situation you find appropriate and demonstrate all three elements of the Newton’s Third Law

in that situation.

c. (6 points) Name one energy system we learned that cannot be negative. Explain why it cannot be negative.

Name one energy system we learned that can be negative. Explain why it is fine for it to be negative.

| | | | page 8

Last Name First Name First three initials of last name

Grade:

11. A ladder of mass mL = 15.0 kg and length L = 5.0 m, which we will assume it is a uniform beam, is leaning

against the wall on the ground. The wall is smooth and frictionless, but the ground is rough. A person

(mp = 40.0 kg) is standing at rest at a distance of 3.0 m above the ground on the ladder. The entire system

is at rest. This problem is very similar to the ladder problem on page 7 of L13.pdf. Follow the prompts and

you will find all the forces acting on the ladder. Recall the static conditions are ΣF~ = 0 and Στ = 0.

a. (8 points) Draw a free body diagram of the ladder+person directly on top of the above diagram.

b. (4 points) Find the vertical component of the force on the ladder by the ground. State which static condition

you are using.

c. (4 points) Find the horizontal component of the force on the ladder by the ground. State which static

condition you are using.

d. (4 points) Finally, find the normal force on the ladder by the wall. State which static condition you are

using.

| | | | page 9

Last Name First Name First three initials of last name

Grade:

12. Water from a water tank flows continuously through a pipe and eventually flows out of a horizontal cylindrical

pipe of 1.0 cm in radius that is placed 2.0 m above the ground. The water level inside the water tank is

assumed to be static and maintained at 30.0 m above the ground. Define point A at the water level inside the

tank, point B at the beginning of the cylindrical pipe, and point C at the end of the cylindrical pipe. Assume

no energy is lost due to non-conservative force. Report all pressure as the absolute pressure.

a. (5 points) Find the pressure at point B (PB). Explain. Hint: Point C is open to the atmosphere and the pipe

is unifom from point B to point C.

b. (5 points) Find the speed of the water at point B (vB). Hint: Find another point where you know the

pressure, fluid speed, and height to use the Bernoull’s equation.

c. (i) (5 points) By what percentage does one need to cover the area of the cylindrical pipe at point C such

that the speed of water at point C is five times than that at point B? That is vC = 5vB.

(ii) (5 points) Find the range of the water (R) if the pipe is covered at point C. Use only the kinematic

equations. Do NOT quote any results about the range in the available resource.

Useful Equations, Formulas, and Constants

Separate this sheet from the text packet. Do not turn it in.

Kinematics in 1D:

∆x = xfinal − xinitial = x − x0

average speed =

distance traveled

time elapsed

average velocity = ¯v =displacement

time elapsed =∆x∆t

instantaneous velocity = v = lim

∆t→0∆x∆t

average acceleration = ¯a =change in velocity

time elapsed =∆v∆t

instantaneous acceleration = a = lim

∆t→0∆v∆t

∆v = vfinal − vinitial = v − v0

v = v0 + at

x = x0 + v0t +12at2v2 = v20 + 2a(x − x0)v¯ =v + v02a = constant

Kinematics in 2D:

~r = x xˆ + y yˆ = (x, y)

~v = vx xˆ + vy yˆ = (vx, vy)

~a = ax xˆ + ay yˆ = (ax, ay)

~v = ~v0 + ~at

~r = ~r0 + ~v0t +12~at2~v2 = ~v02 + 2~ad(d = displacement in the direction of ~a)~a = constant

Forces:

gravity = weight = mg (downwards)

|F~

fr,s| ≤ µs|F~N |

|F~

fr,k| = µk|F~N |

F~

spring = −k~x

Circular Motion:

Energy:WF = Work = F~ · ~r

i = Wtotal

∆KE + ∆PE = Wnon-conservative

∆KE + ∆PE = 0

(When no non-conservative forces)

(1-dimensional elastic collision)

Angular Motion:

(Direction of ~τ given by right-hand rule)

L = Iω (Direction of L~ - right-hand rule)

Moments of inertia:

IPoint Mass = mr2

IHoop = mR2

ISolid Disk = ISolid Cylinder =12mR2