Physics B Section 1 Time 90 Minutes 70 Questions

Physics B Section 1 Time 90 minutes 70 Questions

Directions: Each of the questions or incomplete statements below is followed by five suggested

answers or completions. Select the one that is best in each case and then fill in the

corresponding oval on the answer sheet.

Note: To simplify calculations, you may use g=10 m/s2 in all problems.

31. A solid metal ball and a hollow plastic ball of the same external radius are released from rest in a large vacuum chamber. When each has fallen 1 m they both have the same

(A) inertia (B) speed (C) momentum

(D) kinetic energy (E) change in potential energy

32. A student having a mass of 70 kg starts at rest and accelerates to 3.0 m/s in .50 seconds. What is the rating of this student? P = D KE / time = ½ mv2 / t = ½ (70kg)(3.0m/s-0m/s)2/.50s=

(A) 315 W (B) 420 W (C) 630 W

(D) 2100 W (E) 1260 W

33. A railroad car of mass M is moving at speed v when if collides with a second railroad car of mass m which is at rest. The two cars lock together instantaneously and move along the track. What is the speed of the cars immediately after the collision?

p = po Mv=(M+m)V Mv / ( M+m) = V

(A) v (B) Mv (C) mv

2 m M

(D) m v (E) Mv (M +m) ( m + M )

An open cart on a level surface is rolling without frictional on a level track and loses water through a hole in the bottom of a cart. The velocity of the cart will

(A) increase because of conservation of momentum

(B) increase because of conservation of mechanical energy

(D) decrease because of conservation of mechanical energy

(E) remain the same because the momentum of the system remains the same.

The water leaves with its momentum mwater v

(mcart + mwater) vcartwater = mcart v + mwater v

35. Units of power include which of the following

I. N m/s P = F v = N m/s = kg m/s2 m/s = kg m2 / s3

II. Joule per second P = Work / time = J / s =

III. Kg m2/s2

(A) I only

(B) III only

(D) II and III only

(E) I, II, and III

36. Three forces act on an object. If the object is in translational equilibrium, which of the following is true?

I. The vector sum of the three forces must equal zero. (Defines equilibrium )

II. The magnitudes of the three forces must be equal ( Does not need to be )

III. All three forces must be parallel.(Does need to be )

(A) I only

(B) II only

(D) II and III only

(E) I, II, and III

37. A child pushes on a box of mass m which moves with constant speed v up an incline

The coefficient of friction between the box and the floor is m. At what rate does the child do

work on the box?

Work = F d = (Fgparallel + Ffr)d Work/ time = (Fgparallel + Ffr)d / t Work/time=(Fgparallel + Ffr) v

Work time = ( mgsin f -m m g cos f ) v



A) ( mgsin f -m m g cos f ) v (B) ( mgsin f +m m g cos f )v (C) v /mm g cos f

(D) m mg cos f / v (E) mmg sin f v2

38. An object has a weight W when it is on the surface of planet R. What will be the gravitational

force on the object it has been moved to a distance of 4R from the center of the planet?

A) 16 W (B) 4W C) W D) 1/4 W E) 1/16 W

Fg =G mm The Weight of an object is therefore inversely related to the square of R

r 2

39. This graph represents the potential energy U as a function of displacement x for an object on the end of a spring oscillating in simple harmonic motion with amplitude xo. Which of the following graphs represents the kinetic energy K of the object as a function of displacement?

-xo O xo

(A) (B) K (C) K

-xo O xo -xo O xo -xo O xo

D) (E)

K K

-xo O xo -xo O xo

40. What is the kinetic energy of a satellite of mass m that orbits the Earth, of mass M, in a circular orbit of radius R?

(A) zero (B) 1/2 GMm C) GMm D) GMm E) ½ GMm

R R R2 R2

KE=1/2 mv2 Fg = Fc GmM = mv2 GM = v KE = ½ m( GM )2= ½ mG M

R2 R R R R

0.2 kg

0.1 kg

41.. Two objects of mass 0.2 kg and 0.1 kg respectively, move parallel to the x-axis, as shown above.

The 0.2kg object overtakes and collides with the 0.1kg object. Immediately after the collision, the y

component of the velocity of the 0.1 kg object is 2 m/s downward What is the y-component of the

velocity of the 0.2 kg object immediately after the collision?

(A) 1 m/s upward poy = py = 0 .2kg ( vy) + .1kg ( -2m/s) = 0 vy =+1m/s

(B) .5 m/s upward

(D) .5 m/s downward

(E) 1 m/s downward

Questions 42 and 43

Three objects can move along a straight, level path. The graphs below show the position d of each of

the objects plotted as a function of time t.

d d d

t t t

I II III

42. The magnitude of the momentum is decreasing in which of the cases?

(A) II only (B) III only (C) I and II only

(D) I and III only (D) I, II, and III

43. The sum of the forces on the object is zero in which of the cases?

(A) II only (B) III only

(E) I, II, and III the objects in I and II are moving at a constant velocity therefore

the net force is zero

44. A ball of mass 0.40kg is moving at 2.0 m/s and is pushed from behind and obtains a speed of

5.0 m/s. The magnitude of the impulse imparted on the ball is most nearly

(A) 0.8 N* s impulse = change in momentum = D mv = .40kg ( 5.0m/s – 2.0m/s) = 1.2kgm/s

(B) 1.2 N* s N s = kg m s = kg m/s

(D) 2.8 N *s

(E) 0.0N* s

45. A Person stands on a scale in an elevator. She notices that the scale reading is lower than her normal weight. Which of the following could possibly describe the motion of the elevator?

A) It is moving down at a constant speed. FN = Fg

B) It is moving down and slowing down. FN = Fg + Fnet

C) It is moving up and slowing down. FN = Fg - Fnet

D) It is moving up and speeding up. FN = Fg + Fnet

E) It is moving up with a constant speed. FN = Fg

A rock is thrown horizontally off a building form a height h, as shown. The speed of the rock as it leaves the thrower’s hand at the edge of the building is vo.

46. How much time does it take the rock to travel from the edge of the building to the ground?

(A) h vo

(B) h / vo

(D) 2 h / g

(E) 2 h / g

47. What is the kinetic energy of the rock just before it hits the ground?

(A) 1/2 (mgh)2

(B) m vo2

(D) mgh

(E) mgh + 1/2 mvox2 KEo + mgho = KE + mgh ( since h = 0 )

KEo + mgho = KE

½ mvox2 + mgho = KE

48. Two people of unequal mass are initially standing still on ice with negligible friction. They then

simultaneously push each other horizontally. Afterward, which of the following is true?

(A) The kinetic energies of the two people are equal.(Does not have to be true )

(B) The velocity of the lighter person will be less than the heavier person (opposite is true)

(D) The force that the lighter person puts on the heavier person is equal to the force the heavy person puts on the first ( Conservation of Matter

(E) The less massive person has a smaller initial acceleration than the more massive person.

15 N

49.

12 N

A block of mass 2 kg slides along a horizontal tabletop. A horizontal applied force of 12 N and a vertical applied force of 15 N act on the block as shown above. If the coefficient of kinetic friction between the block and the table is .2. the net force is approximately

A) 1 N B) 3 N C) 4 N D) 5 N E) 7 N

50. The driver of an automobile is initially traveling at constant velocity on a straight road. Due to the sudden appearance of a pedestrian, the driver brakes and decelerates with a magnitude of 15.0 m/s2 in order to avoid a collision. Which one of the following statements concerning the automobile’s motion is correct?

(A) The direction of the acceleration is in the same as the direction of the

displacement.

(B) The direction of the acceleration is the same as the direction of the velocity.

the deceleration.

(D) The automobile travels a distance of 15.0 m during each second of the

deceleration.

(E) The speed of the automobile decreases by 15.0 m/s during each second of the

deceleration. Definition of constant acceleration (deceleration )

51. During a space-walk, an astronaut of mass m pushes on a satellite of mass 2m with a force F The force exerted by the satellite on the astronaut is

(A) 0 (B) -2F (C) 1/2 F (D) – F (E) F

Newton’s 3rd Law Fastronaut on satellite + Fsatellite on astronaut = 0 Newton’s Third Law

52. The graph shows the speed of an object as a function of time. The average speed of

the object during the time interval shown is

Area = displament = ½ bh + bh + ½ bh = [ ½ 10 m/s ( 2s)] + [10 m/s (2s)] + [ ½ 10 m/s (1s) ] = 35m

v = displacement / time = 35 m / 5 s = 7 m/s

(A) 3 m/s (B) 5 m/s (C) 7 m/s (D) 8 m/s (E) 10 m/s

53. What is the total distance traveled by the object in the 5 seconds?

See above – in this case displacement = distance ( this is not always true )

(A) 2.5 m (B) 5.0 m (C) 7.5 m (D) 35 m (E) 37.5 m

Question 54 and 55

v v v v v

t t t t t

(A) (B) (C) (D) (E)

constant acceleration constant velocity decreasing velocity non constant acc non constant acc

54. Which graph best describes the motion of a mass pulled by a constant net force?

(A) (B) (C) (D) (E)

55. Which graph best describes the motion of a mass pulled by a force that is equal to the

frictional acting on it is?

(A) (B) (C) (D) (E)

constant velocity

Question 56. A mass m splits

Before

2/3 m 1/3 m

After

-v

56. The velocity of the 1/3 part after the split is

(A) 1/3 v (B) v (C) 2/3 v (D) 2 v (E) 3 v

po = p= 0 0 = 2/3 m ( - v) + 1/3 m ( ? v ) ? v = 2 v

57. A 70 kg person runs with a horizontal velocity of v and jumps into a 10 kg raft

floating just off shore. Assuming no water resistance, what will be the velocity

of the raft and person?

(A) 1/7 v (B) 7 v (C) 8/7 v (D) 7/8 v (E0 1/8 v

po = p= 70 kg ( v ) = (70kg + 10kg )voverall 70kg v = vorverall 7/8 v = voverall

(70kg + 10kg)

Question 58

The diagram below shows a 10 newton force pulling an 5.0 kg object up a hill at a constant

rate of 4 m / s. The hill is an elevation change of 2 m. Friction should be assumed to be

negligible.

B W = F d = mg h = 5kg (10m/s/s) ( 2 m) = 100 J

10 N

2m 4 m/s

58. How much work is done in moving the object from Point A to Point B

(A) 100 J (B) 120 J (C) 200 J (D) 300 J (D) 1200 J

59 An open railroad car filled with coal is coasting frictionlessly. A girl on board starts