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Final Exam FR Review
SWHS AP Physics Year 1
1.
A 4700 kg truck carrying a 900 kg crate is traveling at 25 m/s to the right along a straight, level highway,
as shown above. The truck driver then applies the brakes, and as it slows down, the truck travels 55 m in
the next 3.0 s. The crate does not slide on the back of the truck.
(a)
Calculate the magnitude of the acceleration of the truck, assuming it is constant.
(b)
On the diagram below, draw and label all the forces acting on the crate during braking.
(c)
i. Calculate the minimum coefficient of friction between the crate and truck that prevents the crate
from sliding.
ii. Indicate whether this friction is static or kinetic.
____ Static ____Kinetic
Now assume the bed of the truck is frictionless, but there is a spring of spring constant 9200 N/m
attaching the crate to the truck, as shown below. The truck is initially at rest.
(d)
(e)
If the truck and crate have the same acceleration, calculate the extension of the spring as the truck
accelerates from rest to 25 m s in 10 s.
At some later time, the truck is moving at a constant speed of 25 m s and the crate is in
equilibrium. Indicate whether the extension of the spring is greater than, less than, or the same as
in part (d) when the truck was accelerating.
___ Greater ___ Less ___ The same
Explain your reasoning.
2.
A ball is attached to a string of length
l swings in a horizontal circle, as shown above, with a constant
speed. The string makes an angle θ with the vertical, and T is the magnitude of the tension in the string.
Express your answers to the following in terms of given quantities and fundamental constants.
(a)
On the figure below, draw and label vectors to represent all the forces acting on the ball when it is at
the position shown in the diagram. The lengths of the vectors should be consistent with the relative
magnitudes of the forces.
(b)
Determine the mass of the ball.
(c)
Determine the speed of the ball.
(d)
Determine the frequency of revolution of the ball.
(e)
Suppose that the string breaks as the ball swings in its circular path. Qualitatively describe the
trajectory of the ball after the string breaks but before it hits the ground.
3.
A series circuit consists of a battery of negligible internal resistance, a variable resistor, and an electric motor of
negligible resistance. The current in the circuit is 2 amperes when the resistance in the circuit is adjusted to 10 ohms.
Under these conditions the motor lifts a l-kilogram mass vertically at a constant speed of 2 meters per second.
a.
Determine the electrical power that is
i. dissipated in the resistor
ii. used by the motor in lifting the mass
iii. supplied by the battery
b.
Determine the potential difference across
i. the resistor
ii. the motor
iii. the battery
The resistor is now adjusted until the mass rises vertically at a constant speed of 3 meters per second. The voltage
drop across the motor is proportional to the speed of the motor, and the current remains constant.
c.
Determine the voltage drop across the motor.
d.
Determine the new resistance in the circuit.
4.
To demonstrate standing waves, one end of a string is attached to a tuning fork with frequency 120 Hz. The other
end of the string passes over a pulley and is connected to a suspended mass M as shown in the figure above. The
value of M is such that the standing wave pattern has four "loops." The length of the string from the tuning fork to
the point where the string touches the top of the pulley is 1.20 m. The linear density of the string is
1.0 x 10-4 kg/m, and remains constant throughout the experiment.
a.
Determine the wavelength of the standing wave.
b.
Determine the speed of transverse waves along the string.
c.
The speed of waves along the string increases with increasing tension in the string. Indicate whether the value
of M should be increased or decreased in order to double the number of loops in the standing wave pattern.
Justify your answer.
d.
If a point on the string at an antinode moves a total vertical distance of 4 cm during
what is the amplitude of the standing wave?
one complete cycle,
“Essay-Style” Questions:
5.
In your summer job with the Department of Transportation and Highways your supervisor has told
you that street signs should no longer be suspended as shown in Diagram A. In order to save
money, he would prefer a shorter, perfectly horizontal cable, as shown in Diagram B.
Using principles of physics, argue that the situation in Diagram B is not reasonable.
6.
Two identical light bulbs, wired in parallel to a battery, are equally bright. When one of the bulbs
burns out, however, the other bulb is observed to glow brighter. Using principles of physics, explain
why the battery causes the remaining bulb to glow more brightly.
7.
Explain why a 6.0 V battery feels warm to touch when it is being used to run a low resistance light
bulb.
KEY:
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1. 2008 Form B #2
2009 #4
2009 #5
2009 Form B #3
2002 Form B #2