Mechanics | Relativity Answers

Vectors A and B are shown in the figure. Vector C is given by C = B - A. The magnitude of vector A is 16.0 units, and the magnitude of vector B is 7.00 units. What is the magnitude of vector C ?

VII. The photoelectric threshold wavelength of a tungsten surface is 272 nm. Calculate the maximum
kinetic energy of the electrons ejected from this tungsten surface by ultraviolet radiation of frequency
1.45 x 1015 Hz. Express the answer in electron volts.

Notes:
Remember that E=hf=hc/λ
Threshold wavelength means the minimum amount of wavelength to remove electrons from a surface
so in this problem, E = = hf ϕ threshold=hc/ λthreshold
where λthreshold = threshold wavelength
= work function = the minimum energy needed to remove an electron from the surface ϕ
h = Planck’s constant = 6.626 x 10 -34 J.s = 4.136 x 10 -15 eV.s
c = 3x108 m/s
f = frequency.

V. Response of the Eye. The human eye is most sensitive to green light of wavelength 505 nm (505
x10-9 m). Experiments have found that when people are kept in the dark room until their eyes adapt to
the darkness, a single photon of green light will trigger receptor cells in the rods of the retina.
(a) What
is the frequency of this photon?
(b) How much energy (in joules and electron volts) does it deliver to
the receptor cells? (c) to appreciate what a small amount of energy this is, calculate how fast a typical
bacterium of mass 9.5x10-12 g would move if it had that much energy.

VI. A photon of yellow light have a wavelength of 560 nm. Find the photon’s frequency, magnitude of
momentum, and energy. Express the energy in both joules and electron volts. ( 1eV=1.602x10-19J)

A woman throws her keys straight up at 8.49m/s. Her friend catches them 2.89m higher. How long were the keys in the air

What will be energy of proton if it is moving with 97% speed of light?

A train is travelling at a speed of 90 km h −1 . Brakes are applied so as to produce a
uniform acceleration of −0.5 m s −2 . Find how far the train will go before it is
brought to rest.

A stone is thrown from the level ground (as in projectile motion). It is observed that the maximum height of
its flight is equal to its horizontal range. Find the launch angle θ0.

A 0.10 kg apple falls from the top of a tree. After falling from the tree, the apple is measured to be traveling at 10 m/s when it is 2.0 m above the ground. How tall is the tree?

A square sheat of steal has a side of 15cm at 00 C. Determine its area at 400C. (Linear expansivity of steel = 1.1x10-5 0C-1

A person standing on a bridge at a height of 115 m above a river drops a 0.250-kg rock. (a) What is the rock's mechanical energy at the time of release relative to the river surface? (b) What are the rock's kinetic, potential, and mechanical energies after it has fallen 75.0