Mr. Walker drove 20 miles to pick up supplies for the Science Olympiad. If the trip to the supply store took 0.75 hours, what was his unit speed for one hour?

On a planet in a different solar system the acceleration of gravity is greater than it is on Earth. If you float in a pool of water on this planet, do you float higher than, lower than, or at the same level as when you float in water on Earth?

A rock falls off a cliff on the Moon. (a) Identify how the motion of the rock differs from the motion of a rock falling from a cliff on Earth. (b) Identify how the motion of the rock is similar to the motion of a rock falling from a cliff on Earth.

Think of an experiment you did in a past science class. a. Describe the experiment. b. What was the experimental variable? c. What were two control variables? d. What was the outcome of the experiment?

Sarah, David, and Ali are friends in science class. The teacher randomly chooses two of the 12 students in the class to work together on a project. What is the probability that two of these three friends will be chosen?

Assume that the solar radiation incident on Earth is $1340 \mathrm{~W} / \mathrm{m}^2$ (at the top of Earth's atmosphere). Calculate the total power radiated by the Sun, taking the average separation between Earth and the Sun to be $1.49 \times 10^{11} \mathrm{~m}$.

Find the indicated velocities and accelerations.

A meteor traveling toward the earth has a velocity inversely proportional to the square root of the distance from the earth’s center. State how its acceleration is related to its distance from the center of the earth.

Light is shining perpendicularly on the surface of the earth with an intensity of

$$680 W/m^2.$$

Assuming all the photons in the light have the same wavelength (in vacuum) of 730 nm, determine the number of photons per second per square meter that reach the earth.

What developments in science, intellectual affairs, and the arts in the late nineteenth and early twentieth centuries "opened the way to a modern consciousness," and how did this consciousness differ from earlier worldviews?

The speed of light is 3 $\times$ 10$^8$ m/s and the distance from Earth to the sun is 1.5 $\times$ 10$^{11}$ m. How many seconds does it take for sunlight to reach Earth? Write your answer in scientific notation.

What is the definition of an astronomical unit? A. the average distance from Jupiter to the Sun B. the average distance from Earth to the Moon C. the average distance from Earth to the Sun D. the average distance from the Sun to the next nearest star.

Another friend says that the Moon's gravity would prevent rocks dropping from the Moon to Earth, but that if the Moon's gravity somehow no longer pulled on its own rocks, then rocks on the Moon would fall to Earth. Explain the wrongness of this assumption.

Analyze the Earth-Sun system by following the Bohr model, where the gravitational force between Earth (mass $m$ ) and Sun (mass $M$ ) replaces the Coulomb force between the electron and proton (so that $F=$ $G M m / r^2$ and $P E=-G M m / r$. Show that (d) Using the Earth-Sun orbit radius of $r=1.49 \times 10^{11} \mathrm{~m}$, determine the value of the quan- tum number $n$.

A rocket goes off to Capella, $45$ light years from Earth, at a $.75$ speed of light and returns to Earth. How long will the trip take both from Earth’s point of view and from the point of view of a person on the spaceship?