Are these true or false, and explain why please.


White light shines on a sheet of iron but does not cause electrons to be emitted from it. Once the intensity of the white light is increased enough electrons will start to be emitted from the iron sheet.

The Bohr model provides a successful explanation for the emission spectrum of hydrogen gas.

Determine your grating constant “d” uncertainty by calculating the standard deviation from the 14 values obtained.

Average grading constant (m)-2.8*10^-6

^Rulling (lines/m)=3.6*10⁵

A person walks into a room that has two flat mirrors on opposite walls. The mirrors produce multiple images of the person. Consider only the images formed in the mirror on the left. When the person is 5.40 m from the mirror on the left wall and 6.70 m from the mirror on the right wall, find the distance from the person to the first three images seen in the mirror on the left wall

First image (m)

Second Image (m)

Third image (m)

Consider a circular vertical loop-the-loop on a roller coaster. A car coasts without power around the loop. Determine the difference between the normal force exerted by the car on a passenger with a mass of m at the top of the loop and the normal force exerted by the car on her at the bottom of the loop.

Express your answer in terms of m and the acceleration due to gravity g.

Two boxes with masses m1=5.0 kg and m2=3.0 kg are connected by a massless rope, which is put over a massless, frictionless pulley. The coefficient of kinetic friction between the incline and the boxes is 0.12 and the coefficient of static friction between the incline and the boxes is 0.25.The angles of the inclines with respect to the horizontal are ?=45** and ?2=30**. Use 9.8 m/s^2 for gravity and assume the incline is fixed in space.

a.) Show that the system will have a nonzero acceleration if it is initially at rest. Find the magnitude and direction of acceleration.

b.) If the system moves 1.5 m(in the direction found in part a), what is the work done by: i.) gravity on m1, ii.) the normal force on m1, iii.) friction on m1, iv.) gravity on m2, v.) the normal force on m2, vi.) friction on m2

c.) Using the results from part b, what is the speed of the system after it has moved 1.5 m if it was initially at rest?

Explain in your own words the transformations that occur at constant pressure and temperature; include all the relevant diagrams.

Under constant pressure, the temperature of 2.00 mol of an ideal monotomic gas is raised 15.0 K. What are a) the work done by the gas b) energy transferred as heat Q c) the change Delta-Eint in the internal energy of the gas, and d) the change Delta-K in the average kinetic energy per atom

A turntable that spins at a constant 77.0 rpm takes 3.50 s to reach this angular speed after it is turned on. Find its angular acceleration (in rad/s^2), assuming it to be constant, and the number of degrees it turns through while speeding up.

A capacitor C is connected to a battery of V volts and is fully charged.Keeping the battery connected, the spacing between the capacitor plates is reduced to half.

What happens to the potential difference between the two plates? Why?

What happens to the charge on the capacitor? Why?

What happens to the energy stored in the capacitor? Why?

Now the battery is disconnected, and then the plate spacing is restored to its original value.

What happens to the potential difference between the two plates? Why?   

What happens to the charge on the capacitor? Why?

What happens to the energy stored in the capacitor? Why?

Note: It is not enough if you say

A 48 g ice cube at -59°C is placed in a lake whose temperature is 57°C. Calculate the change in entropy of the cube-lake system as the ice cube comes to thermal equilibrium with the lake. The specific heat of ice is 2220 J/kg·K. (Hint: Will the ice cube affect the temperature of the lake?)

An object acted on by three forces moves with constant velocity. One force acting on the object is in the positive x direction and has a magnitude of 7.0 N ; a second force has a magnitude of 4.8 N and points in the negative y direction.

a) Find the magnitude of the third force acting on the object.

b) Find the direction of the third force acting on the object.

In February 2013, a 10,000 ton meteor entered the atmosphere near the city of Chelyabinsk, Russia. Analysis of the trajectory showed that the meteor was traveling at a speed of 17.5 km/s at an angle of 17.7o below horizontal, when it was at a height of 77.9 km. Fortunately the meteor exploded high in the atmosphere, where most of its energy was dissipated.

(a) Had the meteor not exploded, and ignoring air resistance, how long would it have taken for the meteor to hit the ground from its 77.9-km height?

(b) With the same assumptions as in part (a), how far in horizontal distance would the meteor have traveled from its initial location to when it hit the ground?

(c) Just before striking the ground, what would have been the meteor’s total velocity? (You may give your answer in either speed-angle or x,y component form.)

A person walks into a room that has, on opposite walls, two plane mirrors producing multiple images. Find the distances from the person to the first three images seen in the left-hand mirror, when the person is 11.0 ft from the mirror on the left wall and 14.0 ft from the mirror on the right wall.

A father (weight W = 849 N) and his daughter (weight W = 394 N) are spending the day at the lake. They are each sitting on a beach ball that is just submerged beneath the water (see the figure). Ignoring the weight of the air in each ball, and the volumes of their legs that are under the water, find (a) the radius of father's ball and (b) the radius of daughter's ball.

A set of crash tests consists of running a test car moving at a speed of 12.6 m/s (27.7 m/h) into a solid wall. Strapped securely in an advanced seat belt system, a 63.0 kg (138.6 lbs) dummy is found to move a distance of 0.720 m from the moment the car touches the wall to the time the car is stopped. Calculate the size of the average force which acts on the dummy during that time.