1. A sled of mass m is pushed for 5 seconds at a constant force. A sled of mass M (more) is also pushed for 5 seconds. THe force is the same in each case. WHat is the momentum of each sled? How do they compare? What is the energy of each sled? How do they compare?

2. The same question, except that each sled is pushed for 5 meters instead of 5 seconds.

You should be able to answer the following questions after studying “Error Analysis of a

Statistical Sample”, found in the Appendices.

a) What is the difference between “random uncertainty” and “systematic uncertainty”?

Provide examples of each.

b) How do you calculate the uncertainty in a set of values that fluctuate randomly about

some mean value?

c) What is the formula for the standard deviation of a sample? What information does the

standard deviation of a set of data provide?

d) What is meant by the phrase “Confidence Interval”?

e) Why is standard deviation used in conjunction with calculating the mean (average) of a

set of data?

LED Lighting BASIC PHYSICS:

a) Give typical forward I-V curves for R-G-B LEDS. Be specific in your three explanations and use manufacturers spec sheets. Also explain why LED lights are both Hg (think bulb breakage effects and land fill issues with dead fluorescent bulbs) and UV free as compared to fluorescents. UV rays cause colors to fade in retail clothing stores, art work to fade in museum lighting and UV accelerates the rancidity of meat fat. UV accelerates the rancidity of meat fat.

b) Explain how and why LED emission takes place over a small solid angle or in simple terms in beam like and unidirectional. Use manufacturer spec sheet plots of emission angles. In contrast fluorescent and incandescent light is omni-directional spread evenly over all 4π sterradians.

A rigid massless rod is rotated about one end in a horizontal circle. There is a load of mass m attached to the center of the rod, and one of mass M attached to the outer end of the rod. The inner section of the rod sustains a tension that is three times as great as the tension that the outer section sustains. The mass ration of m/M is?

Answer is 1

WHY?

(a) Using the definition of the scalar product, find the angles between the following pairs of vectors.

A = 2 i + 3 k and B = - 3 i - 3 j - 5 k    ___°
A = - 5 j and B = - 3 i - 4 j - k    ___°
A = 5 i + 5 j and B = 4 i + 4 j + 2 k    ___°

(b) For A = 2 i + j - 3 k, B = - 2 i + 5 j + 3 k, and C = 2 j - 3 k, find C·(A - B) to three significant figures. ___

Newton's Law of Cooling states that the rate at which and objects cools is directly proportional to the difference in temperature between the object an the surrounding medium. if an object cools from 125F to 100F in half an hour when surrounded by air at a temperautre of 75F, find it's temperature at the end of the next half hour. (Hint: we wrote a differenial equation involving a proportional relationship before in lecture)

Two identical small insulating balls are suspended by separate 0.293 m threads that are attached to a common point on the ceiling. Each ball has a mass of 7.96E-4 kg. Initially the balls are uncharged and hang straight down. They are then given identical positive charges and, as a result, spread apart with an angle of 34.6 ° between the threads. Determine the charge on each ball.

Two soccer players, Mary and Jane, begin running from nearly the same point at the same time. Mary runs in an easterly direction at 4.34 m/s, while Jane takes off in a direction 60.9^o north of east at 5.71 m/s. How long is it before they are 26.7 m apart?

What is the velocity of Jane relative to Mary? Enter first the x-component and then the y-component.

How far apart are they after 3.96 s?

1. a)When applying Newton's 2nd Law to an object on an inclined plane, we choose the coordinate axes parallel and perpendicular to the plane because

it makes the friction force negligible

it means we do not have to split the gravitational force into two components

it makes acceleration along one axis equal to zero

it makes all the forces sum to zero

all of the above

b) The acceleration of an object of mass m down an incline is equal to g*sin(theta)

always

never

only when the mass is light enough to be assumed negligible

only when there is no friction between the mass and the incline

c and d

c) Consider a mass resting on an inclined plane , The magnitude of the normal force

is equal to the magnitude of the weight

is greater than the magnitude of the weight

is less than the magnitude of the weight

is equal to the gravitational field strength, g

a and d

d) A block sitting on an inclined plane starts to slide down the plane when it is inclined at a given angle. To solve foe the coefficient of static friction between the block and the inclined plane, you need:

only the angle

the mass of the block and the angle

the coefficient of kinetic friction

b and c

this is not in the chapter

e) Consider two masses on a frictionless inclined (ideal) Atwood's machine, In order to solve for BOTH the acceleration of the masses and the tension in the string using Newton's second law, we need to know

both masses, the angle, and the normal force

both masses and the angle but not the normal force

both masses but not the angle and not the normal force

it is not possible to solve for both using Newton's second law; an experiment must be done

it is not possible to solve for both using Newton's second law; conservation of energy must be used

Common transparent tape becomes charged when pulled from a dispenser. If one piece is placed above another, the repulsive force can be great enough to support the top piece's weight. Assuming equal point charges (only an approximation), calculate the magnitude of the charge if electrostatic force is great enough to support the weight of a 17.4 mg piece of tape held 0.89 cm above another. (The magnitude of this charge is consistent with what is typical of static electricity.)

7A. Calculations of the primordial material that would form a "quark soup" a few hours after the Big Bang show that the early universe consisted almost entirely of hydrogen (¹₁H = 76 weight %) and helium (⁴₂He = 24 weight %). The present-day atomic ratio of H/He is estimated as 12.5/1. Assuming the present universe consists ONLY of H and He, calculate the present-day wt. % of H and He.

B. Does the present-day wt. % of H and He agree with the Big Bang theory?

C. What physical mechanism(s) explain(s) why the present-day wt. % of H and He does/does not agree with the Big Bang theory?

Intense monoenergetic light source shines on piece of metal. When wavelength of the light is more than 620 nm, no photoelectrons are emitted from metal, and shorter wavelengths begin to produce a flux of photoelectrons. A 248 nm light source is aimed at the same metal, hitting the metal with a power of 0.75 W.

(a) What is the range of energies of photoelectrons produced?

(b) The electrons pass through a single slit, with slit width a= 150 nm and slit perpendicular to the incoming photoelectrons. The photoelectrons travel L=1.5 m before they hit a screen and form an interference intensity pattern. Due to diffraction, what is the width of the MOST energetic photoelectrons on the screen (width = distance between central maximum and first destructive interference)?

Thank you.

You attach a 2.50 kg mass to a horizontal spring that is fixed at one end. You pull the mass until the spring is stretched by 0.500 m and release it from rest. Assume the mass slides on a horizontal surface with negligible friction. The mass reaches a speed of zero again 0.300 s after release (for the first time after release). What is the maximum speed of the mass (in m/s)?

(c7p50) A 1000- kg car collides with a 1300- kg car that was initially at rest at the origin of an x-y coordinate system. After the collision, the lighter car moves at 25.0 km/h in a direction of 25 ^o with respect to the positive x axis. The heavier car moves at 28 km/h at -50 ^o with respect to the positive x axis.
What was the initial speed of the lighter car (in km/h)?

Also, What was the initial direction (as measured counterclockwise from the x-axis)?

1. A 0.25 kg harmonic oscillator has a total mechanical energy of 4.1J. If the oscillation amplitude is 20.0cm. what is the oscillation frequency?

2. A 0.250-kg stone is attached to an ideal spring and undergoes simple harmonic oscillations with a period of 0.640 s. What is the force constant (spring constant) of the spring?

3. An object of mass m = 8.0 kg is attached to an ideal spring and allowed to hang in the earth's gravitational field. The spring stretches 2.2cm before it reaches its equilibrium position. If it were now allowed to oscillate by this spring, what would be its frequency?

4. A 0.39-kg block on a horizontal frictionless surface is attached to an ideal spring whose force constant (spring constant) is 570N/m. The block is pulled from its equilibrium position at x = 0.000 m to a displacement x = +0.080 m and is released from rest. The block then executes simple harmonic motion along the horizontal x-axis. When the position of the block is 0.057m, its kinetic energy is closest to?

Solve by steps and explanation!