Practice+Exam-Part+I

This page will provide explanations for the part I multiple choice questions of the Mechanics Practice exam you received in class. If you have questions or comments about the explanations or would like to add something to the explanation please do so on the specific question.

1. (D) - the slope of the line is velocity. Curves (changing slopes) indicate acceleration. Positive slope or curve = positive acceleration.

2. (D) - displacement is the change in position. The ball starts at a position of 2 m above the ground and ends up on the ground.

3. (B) - Vectors have direction. Acceleration and velocity both have direction.

4. (E) - The greater the angle, the higher in the air a projectile will go. The higher it goes the longer it is in the air.

5. (D) - Once the force is removed, after 1 second, the net force and acceleration of the object are zero.

6. (A) - III is incorrect (it doesn't have to be at rest). IV is also incorrect because it doesn't have to be moving.

7. (A)

8. (D)

9. (D) momentum conservation, p o = p

10. (A) I is wrong because it doesn't conserve momentum in two directions, I I is wrong because all bodies fall at the same rate regardless of horizontal motion and I I I is wrong because the 0.08 kg part would be traveling slower and therefore land closer to the launch point.

11. (A) I  is wrong because only one body is moving linearly, I I is wrong because the collision is completely inelastic.

12. (D) T squared and L have a direct relationship. See the equation for a pendulum and square everything.

13. (B) Angular momentum is conserved in any **closed** system. As the planet approaches the Sun its speed increases but its r decreases (l = rmv).

14. (D) You can eliminate choices A and B since satellite Y must be further from the Earth since it takes longer to complete an orbit. If you set Fc = Fg and solve for r (after substituting v = 2 pi r/T) you will see that r^3 is proportional to T^2.

15. (D) Fg = weight = mg. g = GM/r^2.

16. (E) F = -3t = ma. Solve for a. a = dv/dt, solve for dv and integrate. Solve for v and set equal to zero. Solve for t.

17. (E) smooth parabolic curve that starts above 0.

18. (B) F net = ma. Do this for each block separately and use acceleration given.

19. (D) Solve the two equations you got from question 18 for **T**, then divide the two equations with the M 2 equation on top.

20. (E) Energy conservation

21. (C) a = 0 so net force = 0

22.(C) Area under a F vs t curve = impulse

23. (E) use the equation to find the center of mass(x cm = (m 1 x 1 + m 2 x 2 )/(m 1 +m 2 )), placing the moon at the origin.

24. (B)

25. (D)

26. (E)

27. (C)

28. (C)

29. (B)

30. (C)

31. (A)

32. (E)

33. (E) Springs in series act like "resistors in parallel". 1/k = 1/k1 + 1/k2

34. (C)

35. (E) U = -GMm/R, Energy conservation and W = delta U = integral of F dx