Physics 1112 Spring 2009
Homework #8, due second section of week of
March 9.
Quiz on HW#8 and HW#9 first section
of week of March 30.
Reading: Text 6.4, 7.4, 7.5, 12.4, 8.1 – 8.3
Not all concepts will be covered in class – you are responsible
for all material in the reading and in the homework problems.
1.
A certain midsize car has front crosssectional area
1.8 m
2
, and air drag coefficient 0.30. The density of
air is 1.2 kg/ m
3
.
What is the air drag force (in N) acting on the car
when it is moving at 50 mi/h (= 22 m/s)?
What
power does this drag force dissipate (in kW)?
What
is the air drag force at 65 mi/h (= 29 m/s)?
What
power does this force dissipate (in kW)?
2.
The potential energy of a pair of hydrogen atoms
separated by a large distance x is given by
U(x) = C/x
6
, where C is a positive constant. What is
the force that one atom exerts on the other? Is this
force attractive or repulsive? Give your reasoning,
e.g. do they gain kinetic energy when allowed to
approach each other?
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 Spring '07
 LECLAIR,A
 Force, Work, Bungee, air drag force

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