PHYS 1145 Lecture 1: physics notes 1

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brownferret63

25 Oct 2017

School

Northeastern University

Department

Physics

Course

PHYS 1145

Professor

Brian Spring

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Document Summary

Position: describes where the object is relative to the origin; can be positive or negative. Displacement: net change between two positions; can be positive or negative. Change in x = x nal - x initial. Velocity: a quantity that includes a magnitude & direction; can be positive or negative. Speed: the magnitude of velocity; always positive. Average velocity = change in position over change in time. Instantaneous velocity: velocity at an instant in time. Is equal to the slope of the tangent to the position v time graph at that instant = average velocity over an in nitesimally short time interval.

Related Questions

Coulomb's law for the magnitude of the force F between twoparticles with charges Q and Q' separated by a distance, d is |F| =K *|QQ'|/d2 where K=1/4peo = 8.854*10^-12 nC is the permittivity offree space.

Consider two point charges located on the x axis: one charge, q1 =-19.5nC , is located at x1= -1.680m ; the second charge, q2=31.5nC, is at the origin (x=0.0000).

What is the net force exerted by these two charges on a thirdcharge q3 = 52.5nC placed between q3 and at x3= -1.245m ? Youranswer may be positive or negative, depending on the direction ofthe force.

**Please solve with a numerical answer. I've tried this severaltimes and this is my last attempt on mastering physics.

1. An object is dropped from a height.Once it is moving,which ofthe following statements are true,at least at one point?
a)its velocity is more than its accelerations
b)its velocity is less than its acceleration
c)its velocity is the same as its acceleration
d)its velocity is never equal to its acceleration

2. Which type of quantity is characterized by both magnitude anddirection?
a)scalar
b)vector
c)trigonometric
d)algebraic variable

3. A hiker walks 200m west and then walks 100m north. In whatdirection is her resulting displacement?
a)north
b)west
c)northwest
d)none of the answer is correct

4. Vector 1 is 7 units long and is at 70 degree. Vector 2 is 5units long and is at 225 degree. Vector 3 is a 3 units long and isat 150 degree. Which vector has equal magnitude components?
a)Vector 1
b)vector2
c)vector 3
d)none of the vectors has equal magnitude components??????

5. Which of the following is an example of the type of force thatacts at a distance?
a)gravitational
b)magnetic
c)electrical
d)all of the above

6. A crate weight W is being pushed across a horizontal surface bya force directed at an angle of 20 degrees below the horizontal.What is the magnitude of the normal force on the crate?
a)it is less then W
b)it equals W
c)it is more than W
d)none of the above since the coefficient of kinetic friction isnot given

7. The net force on an object is in the positive x-direction.Consider the following statements.
(i) The object can be moving in the negative x-direction.
(ii) The object can be speeding up.
(iii) The object can be slowing down.
(iv) The object can be moving in the positive y-direction.

Which of the statements are true?
a. (i) and (ii)
b. (ii) and (iii)
c. (iii) and (iv)
d. Choose this answer if all the statements are true.

8.The work done by static friction can be:
a. positive.
b. negative.
c. zero.
d. Any of the above.

9.The rate at which work is done is equivalent to which of thefollowing?
a. increase in potential energy
b. thermal energy
c. potential energy
d. power

10.The dimensional equivalent of the quantity impulse in terms ofthe fundamental quantities (mass, length,
time) is which of the following?
a. MLT-1
b. ML2T-2
c. MLT
d. MLT-2

11. The dimensional equivalence of the quantity "momentum" in termsof the fundamental quantities (mass,
length, time) is:
a. MLT-1.
b. ML2T-2.
c. MLT.
d. MLT-2.

12.In order for a satellite to be geosynchronous, its orbitmust:
a. go over the North and South Poles.
b. be over the equator.
c. be over a single longitude.
d. emit television signals.

13. The quantity "angular momentum" (in terms of the fundamentalquantities of mass, length, and time) is equivalent
to:
a. MLT-2.
b. ML2T-1.
c. ML2T-3.
d. ML3T.
d. MLT-2.

Please refrane from answering if you are unfamiliar with MSExcel and inputing formulas for Cells. Thanks.

NOTE, you may need to save images to desktop to view in a largerscale.

Part b: Collision in Two-Dimensions

The law of conservation of momentum is true for any and everydirection. So, for an isolated system, the momentum in the x, y andz directions or any other direction does not change.

Consider two objects colliding in deep space. Since the two objectstogether can be considered an isolated system, the total momentumof the system (the sum of the momenta of the two objects) isconserved in both the x and y directions. That is

pi-x-total=pf-x-total or pix1+pix2=pfx1+pfx2

pi-y-total=pf-y-total or piy1+piy2=pfy1+pfy2

If we assume object one is moving in the x-direction, object two ismoving in the y-direction and the collision is perfectlyinelastic,
we can rewrite these equations as

m1*vix1=(m1+m2)vfx

m2*viy2=(m1+m2)vfy

These equations can be solved to find the x and y components of theobject's velocity after the collision. The magnitude of vf can befound using the Pythagorean Theorem. The direction of the objectsafter the collision can be found using the inverse cosinefunction

Î¸=cos-1(vfx/|vf|)

Since cos-1 outputs an angle between 0 and Ï radians, we must useÎ¸new=2Ï-Î¸old if vfy is negative to get a correct value. Use thebuilt in function 'if' to find the true value of Î¸. Afterwards,convert the angle into degrees using the built in function'degrees' .

i) Fill in the missing values in the table on the bottom usingformulas to find each value

This is the half of the tablethat is full so far

A = Mass1

B = Velocity initial 1

C = Mass2

D = Velocity intial 2

E = M2/M1

F = Vi2/Vi1

This is therest of the chart that needs formulas

G =Pi-x

H =Pi-y

I =|Pf|

J =Vf-x

K =Vf-y

L =|Vf|

M =Î¸

N = Î¸ if Vi2< 0

O = Î¸(degrees)

PHYS 1145 Lecture 1: physics notes 1

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