91影视

Make a rough estimate of the volume of your body (in${\mathrm{m}}^3$).

The following formula estimates an average person鈥檚 lung capacity V(in litres, where$1\mathrm{L}={10}^3{\mathrm{cm}}^3$):

$\mathrm{V}=4.1\mathrm{H}-0.018\mathrm{A}-2.7$,

Where H and A are the person鈥檚 height (in metres) and age (in years) respectively. In this formula, what are the units of the numbers 4.1, 0.018, and 2.7?

One mole of atoms consists of individual atoms. If a mole of atoms were spread uniformly over the Earth鈥檚 surface, how many atoms would there be per square meter?

Express the sine of$\mathbf{30}\mathbf{.}\mathbf{0}\mathbf{掳}$with the correct number of significant figures.

To convert from ft² to yd², you should

(a) multiply by 3.

(b) multiply by 1/3.

(c) multiply by 9.

(d) multiply by 1/9.

(e) multiply by 6.

(f) multiply by 1/6.

Time intervals measured with a stopwatch typically have an uncertainty of about 0.2 s due to human reaction time at the start a d stop moments. What is the percent uncertainty of a hand-timed measurement of (a) 5.5 s, (b) 55 s, (c) 5.5 min?

Time intervals measured with a stopwatch typically have an uncertainty of about 0.2 s due to human reaction time at the start and stop moments. What is the percent uncertainty of a hand-timed measurement of (a) 5.5 s, (b) 55 s, (c) 5.5 min?

The density of an object is defined as its mass divided by its volume. Suppose a rock鈥檚 mass and volume are measured to 6 g and$2.8325{\mathrm{cm}}^3$. To the correct number of significant figures, determine the rock鈥檚 density (mass/volume).

Recent findings in astrophysics suggest that the observable universe can be modeled as a sphere of radius$\mathrm{R}=13.7脳{10}^9\mathrm{light}\mathrm{years}=13.0脳{10}^{25}\mathrm{m}$with an average total mass density of about$1脳{10}^{-26}\mathrm{kg}/{\mathrm{m}}^3$. Only about 4% of total mass is due to 鈥渙rdinary鈥� matter (such as protons, neutrons, and electrons). Estimate how much ordinary matter (in kg) there is in the observable universe. (For the light- year, see the Problem19.)

Which is not true about an order-of-magnitude estimation?

(a) It gives you a rough idea of the answer.

(b) It can be done by keeping only one significant figure.

(c) It can be used to check if an exact calculation is reasonable.

(d) It may require making some reasonable assumptions in order to calculate the answer.

(e) It will always be accurate to at least two significant figures.