Chapter 1 Review Questions

If you divide a force measured in newtons (1 N = kg • m/s^2) by a speed expressed in meters per second, in what units will the answer be expressed?

(kg • m/s^2) / (m/s) = (kg * m * s) / (s^2 *m) **meters cancel and one s is left on the bottom So kg/s is the answer.

If you square the speed expressed in meters per second, in what units will the answer be expressed?

(m/s)^2 = m^2/s^2

A Hydrogen atom has a diameter of about 10 nm. a. Express this diameter in meters. b. Express this diameter in millimeters. c. Express this diameter in micrometers.

10 nm a = 10 * 10^(-9) m b = 10 * 10^(-5) mm c = 10 * 10^(-4) μm

The height of a horse is sometimes given in units of "hands". Why was this a poor standard of length before it was redefined to refer to exactly 4 in.?

Hands are not a proper way to measure things because every person's hand size is different and you need something consistent like the SI units to measure an object.

Explain the advantages of having the meter officially defined in terms of the distance light travels in a given time rather than as the length of a specific metal bar.

Thermal expansion causes the bar to expand in length (also, thermal contraction causes the bar to shrink). Having the meter measured in this way allows for consistency and can be easily converted.

Can a set of measurements be precise but not accurate? Explain.

Yes. "Precise" means that if you take several measurements, they are very close to each other, even if they are wrong. "Accurate" means that if you take several measurements, the average is close to the correct value, even if the measurements are far apart from each other. Imagine you weigh a 100 lb object 5 times on a precise (but not accurate) scale, and 5 times on an accurate (but not precise) scale. Here are some result you might get: Precise, but not accurate: 112.00, 112.01, 111.98, 112.02, 111.99 Accurate, but not precise: 100, 95, 105, 90, 110

How many significant figures are there in the following measurements? a. 78.9 ± 0.2 m b. 3.788 * 10^9 s c. 2.46 * 10^6 kg d. 0.0032 mm

a. 3 sig. figs. b. 4 sig. figs. c. 3 sig. figs. d. 2 sig. figs.

Einstein's famous equation indicates that E=mc^2, where c is the speed of light and m is the object's mass. Given this, what is the SI unit for E?

m has kg unit, c is m/s so kg(m/s)^2 = kgm^2/s^2 **note that 1N=kgm/s^2 So we have kgm/s^2 * m, which is N*m. N*m = J (Joule).