Resistance Exercises
1. You need to push your lab table away from the
wall. Why is it harder to start the table sliding
than it is to keep the table sliding when it is
moving?
7. The forces acting on four objects moving through a
fluid are shown below. The force vectors are drawn
to scale. Which object(s) moves at a constant
velocity?
2. Suppose you drop an empty water bottle and an
identical full water bottle from the same height.
Explain which bottle will hit the ground first?
8. The volume flow rates and pressure drops for two
pipes are graphed below.
3. When you push on the car brakes, friction
between the wheels and the road create a force
that pushes opposite the direction of the car.
(a) Will the friction be greater when the tires
continue to roll to a stop, or when the tires
“lock” and start to skid?
(b) If more people were in the car, explain if
that would increase or if it would decrease the
maximum braking force.
____ (a) Which pipe has the highest resistance?
____ (b) If the pipes are the same length, which one
has the larger diameter?
____ (c) If the pipes have the same diameter, which
one is longer?
(c) If it starts raining, explain if that would
increase or if it would decrease the maximum
braking force.
9. The two water pipes shown below have the same
diameter and length. The water flow rate through the
pipes is the same, but the pressure drop is not the
same. Explain what could cause the difference in
pressure drop?
4. The drag on an object moving through a
stationary fluid _________________ (increases
or decreases) as the object’s speed increases.
5. If a fluid flows past a stationary object, the drag
on the object _________________ (increases or
decreases) as the fluid’s speed increases.
6. Fluid resistance increases as flow becomes
________________ (laminar or turbulent).
10. Electrical resistance in a wire is a measure of
the opposition to the flow of ______________.
11. Are copper wires and metallic solder
conductors, semiconductors, or insulators?
16. (a) What is the total current through the parallel
circuit shown below?
(b)What is the voltage drop across each resistor?
(c) What is the current through each resistor?
12. The resistance of a wire does not depend on
which of the following?
(a) wire material
(b) wire mass
(c) wire cross-sectional are
(d) wire length
13. The resistivity of a wire depends on
(a) wire material
(b) wire mass
(c) wire cross-sectional are
(d) wire length
14. The graph below shows the relationship
between current and voltage for two resistors.
Which resistor has the greater resistance?
17. Thermal resistance is the opposition to the flow of
_______________________.
18. Thermal resistance is the ratio of _______________
to ___________________.
19. If temperature is measured in ºC and heat flow is
measured in cal/s, what are the units of thermal
resistance?
15. (a) What is the current through each resistor in
the series circuit shown below?
(b) What is the voltage drop across each
resistor?
20. The thermal conductivity of a material depends on
(a) thickness of the material
(b) type of material
(c) temperature difference across the material
(d) surface area of the material
21. An architect designs an office building with large
windows. Each window has length L, width W, and
thickness Δx. How can the architect reduce the heat
flow rate through each window?
(a) us a material with a higher thermal conductivity
(b) increase L and /or W
(c) increase Δx
(d) all of the above
22. A wall has three layers with resistances of R1, R2,
and R3. How would you calculate the total
resistance?