Which of the following might be measured in
square meters?
a. the length of a pendulum string
b. the volume of an atom
c. the mass of a book
d. the area of a desk top

The correct answer to this question is D. The area of a desk top.

Explanation:

Square meters, or m^2, are the units that represent area, or the product of two lengths.  This is because the length and the width both have the units meters, so when multiplied to calculate area, the resulting units are square meters or m2.  Thus, the answer for this question is D.

The length of a pendulum string would be measured in meters.

The volume of an atom would be measured in m^3 (volume is the product of the length, width, and height, giving it a cubic power).  However, the volume would probably be measured in a much smaller unit because atoms are very small.

The mass of a book would likely be measured in grams or kilograms.

A. The length of a pendulum string . . . No. Square meters is not a unit of length.  That would be multiples or fractions of a meter.

B. The volume of an atom . . . No. Square meters is not a unit of volume.  That would be multiples or fractions of a cubic meter.

C. The mass of a book  . . . No. Square meters is not a unit of mass.  That would be multiples or fractions of a kilogram.

D. The area of a desk top . . . YES !  Square meters is a unit of area.

the duration of a photographic flash is related to an rc time constant, which is 0.100 μs for a certain camera.

see the picture for the vector

the magnitude of the vector by pythagorean theorem

r = √( (-10)^2 + (3)^2 ) = √109

magnitude = √109 units

the direction angle between vector and x-axis is

tan^(-1)(3/10) = 16.699

so the direction is approximately 16.7 degrees north of west