Phy 121 - Assignment 12
A. 1. a. BTU (British Thermal Unit)
b. calorie
2.
B. 1. 100° water only gives off heat due to changing temperature. 100° steam
gives off that heat from changing temperature plus the heat from its change of
state. The extra heat (which is quite a bit more) makes the burn worse.
2.
C. 1. Why: to allow for expansion and contraction.
Wood & Aluminum don’t expand and contract nearly as much. (You can see
that by looking up their expansion coefficients on the table in the formula
sheet.)
2.
D. 1. Steel makes the larger hole. With equal masses and equal temperature
changes, the one with the larger specific heat gives off more heat, melting more
ice. (Look up specific heats in formula sheet.)
2.
(Some people work with the wheel’s circumference instead of its diameter,
thinking that you’ve actually got iron around the circumference, but the
diameter is just a hole made out of nothing. That approach is not incorrect, just
a little more complicated. It follows from C = πd that the change in the
circumference is proportional to the change in the diameter, so you might as
well work with the diameter. ΔL = L0  ΔT works for any dimension of an
object, measured through solid material or not.)
E. 1. Water’s temperature increases about half as much . (Rearranging Q = m
c ΔT, ΔT = Q/(m c). With Q and m the same, that’s an inverse proportion
between ΔT and c. Twice the c means half the ΔT.)
2.
F. a. Point-like particle following an orbit of radius r: I = mr2
Total I = (.0018 kg)(.55 m)2 + (.0018 kg)(.10 m)2 +(.0018 kg)(.45 m)2
= .0005445 + .000018 + .0003645 = .000927 kg·m2
KE = ½ Iω2 = ½(.000927)(10)2 =
.0463 J
b. Cylinder rotating about its center: I = ½ MR2
Total I = ½(.0018 kg)(.003 m)2 + ½(.0018)(.003)2 + ½(.0018)(.003)2
= (3)(8.1 x 10-9) = 2.43 x 10-8
KE = ½ Iω2 = ½(2.43 x 10-8)(10)2 =
1.21 x 10-6 J