Download Practice Exam – Final

Practice Exam – Final
April 25th
1. The figure on the board shows the overhead view of two stones that travel in circles
over a frictionless horizontal surface. Each stone is tied to a cord whose opposite end is
anchored at the center of the circle. The radius of the circle of stone B is 3 times the
radius of the circle of stone A. The tension in the long cord is 4 times the tension in the
short cord. The period of stone B is 2 times the period of stone A. What is the ratio:
(mass of stone B):(mass of stone A)
(A) 9:16
(B) 3:16
(C) 36:16
(D) 3:4
(E) 1:16
2. City B is 800km east of city A. A light plane can fly at a speed of 300km/hr with
respect to the air. If there is a constant wind at a speed of 250km/hr blowing in a direction
25° north of east, what is the time it takes for the plane to make the trip from A to B?
(A) 2.67 hr
(B) 2.00 hr
(C) 1.58 hr
(E) The trip as described is not possible.
(D) 1.45 hr
3. Ball A is dropped from the top of a building of height h at the same instant that ball
B is thrown vertically upward from the ground. When the balls collide, they are moving
in opposite directions, and the speed of A is three times the speed of B. How far above
the ground does the collision occur?
(A) 5h/6
(B) 5h/8
(C) h/2
(D) 2h/3
(E) h/6
4. A 25-g rubber ball bounces on a table as shown in the figure on the board. The ball
and the table are in contact for 10 ms. What is the magnitude of the average force exerted
on the ball by the table?
(A) 0 N
(B) 60 N
(C) 120 N
(D) 160 N
(E) 200 N
5. Several forces F are applied to the 2D objects depicted on the board. All forces have
equal magnitude. All the objects have the same mass, uniformly distributed. Which of the
following statements about the magnitude of the angular acceleration about the center of
mass of each system is true?
(A) αP <αR<αQ (B) αP <αQ<αR (C) αP =αQ<αR (D) αP <αR<αQ
(E) αP <αQ=αR
6. A system consists of two identical solid disks of mass M and radius R attached
together as shown below. What is the moment of inertia of the system about an axis
perpendicular to the page at point P?
(A) 13MR²
(B) 7MR²
(C) 6MR²
(D) 4MR²
(E) 3MR²
7. The figure on the board shows blocks of mass m attached to pulleys of mass m with an
ideal string which pulls without slipping. Which is the correct ranking for the acceleration
of the blocks?
(A) aP <aQ<aR (B) aQ <aR<aP (C) aP =aQ<aR (D) aR =aQ<aP (E) aP <aR<aQ
8. In the circuit on the board, R1 = 20 Ω, R2 = 40 Ω, R3 = 60Ω and V0 = 240 V. Determine
the magnitude of the current through R1.
(A) 1.4 A
(B) 1.8 A
(C) 2.2 A
(D) 2.7 A
(E) 3.2 A
9. Four identical bulbs are connected in a circuit with an ideal battery as shown on the
board. Rank the brightness B of the bulbs:
A. B1 > B2 > B3> B4
B. B4 > B3> B2 = B1
C. B1 > B3 > B2> B4
D. B1 = B2 > B3 = B4
E. B1 = B2 < B3 = B4
10. Which of the following statements about equipotential surfaces (EPS) is true?
A. The electric field is always parallel to the EPS’s.
B. The electric field lines are always parallel to the EPS’s.
C. The electric flux through an EPS is never zero.
D. The surface of an insulator in equilibrium is an EPS.
E. The EPS’s of a point charge are concentric cylinders.
11. Two infinite parallel conducting plates carrying charge densities σ and
−σ are separated by a distance d. Let E1 be the magnitude of the electric field half way
between the two plates. In Figure 2 the two identical plates are separated by a distance
2d and the electric field half way between the plates is E2. What is the ratio between E1
and E2?
(A)E1:E2=4:1 (B)E1:E2=2:1 (C)E1:E2=1:1 (D)E1:E2=1:2 (E)E1:E2=1:4
12. A particle with charge 3mC and mass 2kg is in a uniform electric field directed to the
left. It is released from rest and moves to the left; after it has moved 1m, the velocity of
the particle is 4m/s. What is the magnitude of the electric field?
(A) 70 V/m
(B)700 V/m
(C)1300 V/m (D)4700V/m (E)5300V/m
13. In the circuit shown, what is the power dissipated by the 4Ω resistor?
(A) 15W
(B)32W
(C)53W
(D)106W
(E)212W
14. A parallel plate capacitor consists of two plates separated by a distance d. It is
attached to a battery and an amount of energy U is stored in the capacitor. While it is
connected to the battery, the distance between the two plates is increased to 3d. What is
the energy stored in the capacitor after the distance is increased?
(A) U/3
(B) U/6
(C) U
(D) 3U
(E) 9U
15. A capacitor consists of two circular disks of radius 20cm which are separated by a
distance of 4mm. What is the capacitance?
(A) 28 pF
(B) 140 pF
(C) 28 nF
(D) 70 pF
(E) 278 pF
16. A projectile is fired from the Moon’s surface at exactly the escape velocity in a
horizontal direction as shown. It passes points P and Q where RP and RQ are the
distances between each point and the center of the Moon. Likewise, vP and v Q are the
velocities of the projectile as it passes points P and Q respectively, if RQ= 2RP, what is the
ratio vQ : v P ?
(A) √2 :1
(B). √2:2
(C) 1: 2
(D) 1: 2 √2
(E) 1:4
17. The ends of a wire whose cross-section is a square of side a = 1.45 mm and length l =
40.0 m. The current flowing through the wire is measured to be I = 2.2 A. The density of
free electrons is n= 9.0 x 10^28 electrons/m³. How long does it take (hr) for an electron
to travel the length of the wire? (Assume the electrons are moving at drift speed.)
(A) 12 hr
(B) 86 hr
(C) 108 hr
(D) 153 hr
(E) 9200 hr
18. As in the Collision in Two Dimensions lab, consider two air pucks sliding with little
friction on a smooth, level surface. Assume they are each moving with some velocity,
collide, and then one subsequently rebounds from the edge of the table. Consider the
total vector momentum, P, of the two pucks (only). Let P1 be its value before the collision
of the pucks, P2 its value after collision, and P3 its value after one of the pucks hits the
edge of the table. Which of the following most accurately describes the relationship
between these quantities?
(A) P1 = P2 = P3
(B) P1 = P2 ≠ P3
(C) P1 ≠ P2 = P3
(D) P1 ≠ P2 ≠ P3
(E) Without knowing whether the collisions are elastic, one cannot say.
19. Consider the motion of a cart like the one you used in lab, and which is adjusted to
have significant frictional drag. Assume that the friction is well described by the "laws"
of (dry) friction that you studied this semester. Also assume that the cart is given an
initial velocity toward the left on the horizontal track and then released. (Assume the
sensor gives positions relative to the X axis illustrated in the figure). Which of the
following graphs best illustrates the velocity, VX , of the cart versus time after it leaves
your hand?
20. As done in lab, a student, seat, chain, and two load cells are at rest and supported by
cables attached to the upper (sensitive) fittings of the two load cells. The cell readings
and those of the large protractors are given in the table below.
Cell reading
Protractor reading
LEFT
414 N
63°
RIGHT
506 N
48°
Use this information to estimate the total force in the Y direction exerted by the two
cables together on the student, seat, chain and cells.
(A) 527 N
(B) 707 N
(C) 745 N
(D) 564 N
E) 0 (The total force must be zero, since nothing is accelerating.)