Spring 2005
MWF 11:30
Instructor: Dr. Bruce Law, CW
327, Tel: 532-1618.
REVIEW QUESTIONS OF Home Work 10
R7. Heat
energy travels from your hot hand to the cold surface. This occurs via the
process of conduction, where the molecules of your hot hand (which are
vibrating faster because they are hotter) bang into and transfer energy to the
slower moving molecules of the cold surface.
R10. The temperature difference of two objects. Heat always flows
from the hot object to the cold object.
R15. Q
= mcDT
therefore DT = Q/(mc).
Therefore DT is large (and the object heats up
quickly) if c is small.
R16. DT = Q/(mc), therefore, DT is large (and the cools down quickly) if c is small.
E10. Yes, but
the amount of water in the
E11. The
temperature at the bottom of the falls is expected to be slightly higher than
the temperature at the top of the falls because the GPE at the top is converted
to KE at the bottom, which in turn is transformed into heat energy when the
falling water is stopped.
E13. Q = mcDT therefore DT = Q/(mc). For a given
amount of heat (Q) the temperature change DT
depends upon the mass m and the heat capacity c of the object. For example, for
small m and c then DT will be large,
conversely, for large m and c then DT will be
small.
E15. Water has
a high heat capacity c i.e. it usually takes a long time to heat up or cool
down. The water mellon is
mostly water; it also has a much larger mass than the sandwiches. Therefore for
the water mellon as DT = Q/(mc) where both m and c
are large it will require a lot of heat Q in order to change the temperature of
the water mellon significantly – the water mellon will therefore stay cool over a longer period of
time compared with the sandwiches.
E18. Water has
a large heat capacity therefore it takes a long time to heat up or cool down.
By contrast land heats up or cools down very quickly. In hot weather, land
becomes hot very quickly but a large water mass remains relatively cool
compared with the land, hence, a large water mass cools the land. In cold
weather, land becomes cold very quickly but a large water mass remains
relatively warm compared with the land, hence, a large water mass warms the
land.