1. Intro to Physics Units

The age of the universe is thought to be about 14 billion years. Assuming two significant figures, write this in powers of 10 in years.

The Sun, on average, is 93 million miles from Earth. How many meters is this? Express using a metric prefix (km).

An alien spacecraft is flying overhead at a great distance as you stand in your backyard. You see its searchlight blink on for $0.150$ s. The first officer on the spacecraft measures that the searchlight is on for $12.0$ ms.

(a) Which of these two measured times is the proper time?

(b) What is the speed of the spacecraft relative to the earth, expressed as a fraction of the speed of light $c$?

The positive muon (µ⁺), an unstable particle, lives on average 2.20 × 10^-6 s (measured in its own frame of reference) before decaying. What average distance, measured in the laboratory, does the particle move before decaying?

The positive muon (µ⁺), an unstable particle, lives on average 2.20 × 10^-6 s (measured in its own frame of reference) before decaying. If such a particle is moving, with respect to the laboratory, with a speed of 0.900c, what average lifetime is measured in the laboratory?

A force is applied to a particle along its direction of motion. At what speed is the magnitude of force required to produce a given acceleration twice as great as the force required to produce the same acceleration when the particle is at rest? Express your answer in terms of the speed of light.

A proton has momentum with magnitude p₀ when its speed is 0.400c. In terms of p₀, what is the magnitude of the proton's momentum when its speed is doubled to 0.800c?

Suppose the two lightning bolts shown in Fig. 37.5a are simultaneous to an observer on the train. Show that they are not simultaneous to an observer on the ground. Which lightning strike does the ground observer measure to come first?

X rays with initial wavelength $0.0665$ nm undergo Compton scattering. What is the longest wavelength found in the scattered x rays? At which scattering angle is this wavelength observed?

The cathode-ray tubes that generated the picture in early color televisions were sources of x rays. If the acceleration voltage in a television tube is $15.0$ kV, what are the shortest-wavelength x rays produced by the television?

The photoelectric work function of potassium is $2.3$ eV. If light that has a wavelength of $190$ nm falls on potassium, find the kinetic energy, in electron volts, of the most energetic electrons ejected.

The photoelectric work function of potassium is $2.3$ eV. If light that has a wavelength of $190$ nm falls on potassium, find the stopping potential in volts.

What would the minimum work function for a metal have to be for visible light ($380$–$750$ nm) to eject photoelectrons?

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 $1.45\times {10}^{15}$ Hz. Express the answer in electron volts.

A photon has momentum of magnitude $8.24\times10^{-28}$ kg-m/s. What is the wavelength of this photon? In what region of the electromagnetic spectrum does it lie?