Which process causes river gravel to have rounded edges? A. abrasion B. acid rain C. ice wedging D. oxidation

Suppose that the elevation on a hill is given by $f(x, y)=100-4 x^{2}-2 y$. From the site at (2, 1), in which direction will the rain run off?

A football, in the shape of an ellipsoid, is lying on the ground in the rain. Its length is 8 inches and its cross section at its widest point is a circular disc of radius 2 inches. A rain drop hits the top half of the football. Find the path that it follows as it runs clown the top half of the football. Hint: Recall that the gradient of a function f(x, y) points in the (x, y) -direction of maximum increase of f.

Calculate the $\mathrm{pH}$ of a sample of acid rain that has $\left[\mathrm{OH}^{-}\right]=2 \times 10^{-10} \mathrm{M}$.

Which of the following could be a result of a change in the Earth’s albedo?

(a) nitrogen oxides

(b) acid rain

(c) photochemical smog

(d) particulate matter

Calculate the hydraulic radius for the section shown in the given figure if water flows at a depth of $3.50\ \mathrm{in}$. The section is that of a rain gutter for a house.

Identify A model of the erosion cycle shows

a. the processes of pollution and rain

b. the processes of erosion and deposition.

c. surface area.

d. climate.

When a tropical rain forest is cleared, why does the soil usually become useless for growing crops after only a few years?

A spherical rain drop of radius 1.0 nun has a charge of +2 nC. The electric field in the vicinity is 2000 N/C downward. The terminal speed of an identical but uncharged drop is 6.5 m/s. The drag force is related to the drop's speed by $F _ { \mathrm { d } } = b v ^ { 2 }$ (turbulent drag rather then viscous drag). Calculate the terminal speed of the charged rain drop.

Each of the following sentences contains an error in the use of tenses. Rewrite the sentences to correct the errors.

EXAMPLE: Once the rain stopped, we had a picnic. Once the rain had stopped, we had a picnic.

Because fire ants' stings were painful, we were especially careful to avoid ant mounds when we worked in the yard yesterday.

The beaks of finches on the Galapagos Islands enlarged over generations in response to

A isolation.

B pollution.

C rain.

D limited food supply.

Suppose that the elevation on a hill is given by $f(x, y)=200-y^{2}-4 x^{2}$. From the site at (1, 2), in which direction will the rain run off?

Consider a situation in which acid rain has heavily polluted a lake to a level of $\mathrm{pH}\ 4$. An unscrupulous chemical company dumps some acid into the lake illegally. Assume that the lake contains $100$ million gallons of water and that the company dumps $100,000 \mathrm{gal}-$ lons of acid with $\mathrm{pH}\ 2$.

a. What is the hydrogen ion concentration, $\left\lfloor\mathrm{H}^{+}\right\rfloor$, of the lake polluted by acid rain alone?

b. Suppose that the unpolluted lake, without acid rain, would have $\mathrm{pH}$ $7$. If the lake were then polluted by company acid alone (no acid rain), what hydrogen ion concentration, $\left[\mathrm{H}^{+}\right]$, and $\mathrm{pH}$ would it have?

c. What is the hydrogen ion concentration, $\left[\mathrm{H}^{+}\right]$, after the company dumps the acid into the acid rain-polluted lake ( $\mathrm{pH} 4)$ ? What is the new $\mathrm{pH}$ of the lake?

d. If the U.S. Environmental Protection Agency can test for changes in $\mathrm{pH}$ of only $0.1$ or greater, could the company's pollution be detected?

In each sentence, underline the subject and the correct form of don't or doesn't in parentheses.

It (don't, doesn't) rain much in the Atacama Desert in Chile.