Physics Practice Exam 2

Physics Practice Exam 2

March 28

1. Particles P, Q, R and S are moving in the +x direction. The momenta and kinetic

energies of these particles are given in the table below. Which is the correct ranking of

the speeds of these particles?

Particle Kinetic Energy Momentum

P K0 p0

Q 2K0 p0

R K0 2p0

S 2K0 2p0

(A) vR>vP>vS>vQ

(B) vR>vS>vP>vQ

(C)vQ>vP=vS>vR

(D) vQ>vS>vP>vR

(E) None of the above

2. If a collision between two particles is inelastic, which of the following statements is

false?

(A) The total kinetic energy is conserved.

(B) The total momentum is conserved.

(D) The total kinetic energy is reduced by the collision.

(E) The total angular momentum of the system is conserved.

3. A 4kg block is sliding to the right along a frictionless horizontal surface. Initially the

kinetic energy of the block is 38J. It encounters an incline that slopes upwards at an angle

of 30º. The coefficient of kinetic friction between the block and the incline is μk= 0.72

What is the maximum distance, d, which the block slides up the ramp before coming to a

stop?

(A) 62cm (B) 71cm (C) 79cm (D) 86cm (E) 97cm

4. A small 0.8-kg ball is pressed against a vertical spring of negligible mass. The spring is compressed x= 4.0 cm from its relaxed position. When the system isreleased from rest, the ball is shot up in the air and reaches a maximum height of h = 3.4m above its initial position. Determine the force constant k of the spring. Neglect air resistance.

(A) 33 N/m (B) 33 kN/m (C) 1300 N/m (D) 45 kN/m

(E) The ball can never reach that height.

The following applies to the questions 5 and 6: A particle of mass m = 2 kg

moves along the x-axis under the influence of a single force whose associated potential

energy is depicted in the figure on the board. At t = 0, the particle is released at a velocity of 3 m/s at x = 4 m.

5. How close to the origin will the particle get?

(A) About 2 m

(B) 4 m

(D) About 6 m, because the particle will not move since U(6 m) = 0 J.

(E) 12 m

6. What is the maximum velocity of the particle?

(A)0 (B) 6.67 m/s (C)13.34 m/s (D)8.6m/s(E)9.4 m/s

7. A solid cylinder of mass m=30kg, length L=1.0m and radius R=0.5m and uniform

density is lying on its side with the axis parallel to the ground. How much net work must

be done to tip it to the vertical so that the axis is perpendicular to the ground?

(A) 29J (B)59J (C) 118J (D) 147J (E) 0J

8. A horizontal disk of radius R and mass M rotates with an angular speed ω. Another

disk with the same axis, radius R/3, mass 2M and no initial speed is dropped on top of the first one. What is the final angular velocity, ωf, of the two disk system when the disks stop rubbing and rotate as a single unit. Assume that there is no friction on the axel or other external torques.

(A) ωf =9ω/11(B) ωf =2ω/3 (C) ωf =ω(D) ωf =9ω/10(E) ωf =2ω

9. The horizontal beam in the figure on the board is massless and is hinged to a vertical wall as shown. If the box has a mass of 40 kg, what is the tension in the 7m wire?

(A) 250N(B) 463N(C) 500N(D) 543N(E) 600N

10. A wooden rod of uniform density, length 1m and mass 3kg is suspended with a frictionless hinge in the middle and hangs motionless. A bullet of mass 3g hits the rod and the angular velocity after the bullet hits is 0.80 rad/s. What is the velocity of the bullet when it strikes?

(A) 142 m/s(B) 200 m/s(C) 241 m/s(D) 340 m/s (E) 445 m/s

11. A 5.0 kg rock is attached to a freely hanging from a string of length 2 m, which is attached to the ceiling. If the string is pushed so it dangles back and forth in a periodic motion, what is the period of its oscillation?

(A) 1.42 s(B) 2.21 s (C) 2.84 s(D) 4.42 s (E) 6.28 s

12. If the string, at the top of its swinging motion, makes an angle of 40 degrees with the ceiling, what will be the highest speed the rock will reach in its motion?

(A) 1.87 m/s(B) 3.74 m/s (C) 5.29m/s(D) 6.26 m/s (E) 8.85 m/s

13. Sarah throws a 90g snowball at John who is in a tree. Sarah releases the snowball at

an angle of 70º to the horizontal at a speed of 25m/s from a point 1.5m above the ground.

The snowball strikes John who is 12m above the ground. How fast is the snowball traveling when it strikes John? Neglect air resistance.

(A) 16.5 m/s (B) 18.3 m/s (C) 19.7 m/s (D) 20.5 m/s

(E) The snowball cannot reach John given the information in the problem.

14. In the figure on the board, a horizontal rod of uniform density with weight 55N and length 4.4m is attached to a wall with a frictionless ideal hinge. If the rod is released at rest, what is the angular acceleration of the rod about the hinge just after it is released?

(A) 0.34 rad/s²(B) 3.34 rad/s²(C) 6.68 rad/s²(D) 9.80 rad/s²(E) 26.7 rad/s²

15. A 400-g particle attached to a spring with k = 100 N/m is also subject to a damping force F = − bv, where v is the velocity of the particle and b = 13.0 kg/s. Which of the graphs shown on the board best represents the kinetic energy of the particle as a function of time?

16. A math book (1.5 kg) is dropped from the top of the EmpireStateBuilding (about 381 m high). What is the magnitude of the average force it exerts on the ground if it is in contact with the ground for 0.2s before coming to a complete stop? Neglect air resistance.

(A) 207N (B) 324N (C) 648N (D) 917N (E) 1396N

17. If a particle has a momentum vector p=(2i – j + k)Ns and radius vector r=(-i + 3j - 2k)m, what is the angular momentum about the origin?

(A) L=(i – 3j – 5k)Js(B) L= (5i – 3j + k)Js(C) L= (-2i - 3j + 2k)Js

(D) L= (3i – 4j +k)Js(E) L= (i + j – k)Js

18. A 2.0 kg mass is attached to the end of a spring and moves in simple harmonic motion without damping. If the period of the motion is 3s, what is the spring constant, k, of the spring?

(A) 0.22N/m (B) 0.95N/m (C) 4.39N/m(D) 8.77N/m (E)18.0 N/m

19. Say we now attach the 2.0 kg mass to a different spring of spring constant k= 4.80 N/m, and a damping force acts on the spring. When the mass is moving 3 m/s, the magnitude of the damping force is 4 N. What is the new angular frequency of the system, ω’?

(A) 0.70 rad/s(B) 1.40 rad/s(C) 1.51 rad/s(D) 2.80 rad/s(D) 3.10 rad/s

20. A 5m long plank of weight 120N and uniform density rests on two scales which measure force in Newtons. Scale #1 supports a point 0.8m from the left hand end of the plank while scale #2 supports a point 0.2 m from the right end of the plank. What are the readings of the two scales?

(A) Scale 1 reads 80N; Scale 2 reads 40N

(B) Scale 1 reads 60N; Scale 2 reads 60N

(D) Scale 1 reads 56N; Scale 2 reads 64N

(E) Scale 1 reads 70N; Scale 2 reads 50N