## Saturday, February 15, 2014

### GRE Sample Physics Problems (5)

The diagram (Fig. 1) shows a resting cylinder of weight W. The coefficient for static friction for all surfaces is 1/3.  The applied force for P = 2W

61)The distance d for which the counterclockwise motion is initiated by P is:

A) d = r/3    B) d = d/2   C) d = r/ 4  D) d = 2d/ 5   E) d = 3r/ 5

62) The vertical reaction force at point A is:

A)    0.3 W  …B)0.5W…..C) 0.8W…. D) 0.9 W…..E) 1.5W

63) The vertical reaction force at point B is:

A) 3W…..B) 2.7 W……C) 1.5 W…..D) 2.1 W….E) 2.5 W

64) The horizontal reaction force at point A is:

A) 1.5 W…..B) 2.1 W….  C) 0.9 W……D) 1.2 W……E) 1.8 W

65) The horizontal reaction force at point B is:

A) 1.5 W…..B) 02.1 W…..C)  0.9 W….D) 1.2 W…..E) 1.8 W

66) If the frequency of the sound produced by a siren increases from 400 cps to 1200 cps while the wave amplitude remains constant, the ratio of the intensity of the 1200 cps wave to the 400 cps wave is:

A) 1: 1…..B) 1: 3…..c) 3: 1……D) 1: 9 ….E) 9:1

67) A stream of water leaving the nozzle of  a hose horizontally 4 feet above the ground strikes the ground at a horizontal distance of 20 feet. The velocity of the water when leaving the nozzle, in feet per second, is:

A) 20…..B) 30……C) 40……D) 60……E) 80

68) A wire of length L has a cross-sectional area A and Young’s modulus Y. The force constant should be equal to:

A) YA/ L……B)  A/ YL……C) Y……D) L/YA   …E) Y/A

69) A battery is connected to a resistor causing a current of 0.6 amps to flow. When an additional 4.0 ohm resistor is added in series to the circuit, the current drops to 0.5 amp. The emf of the battery is:

A) 5 volts….B) 6 volts…..C) 12 volts…..D) 4 volts…..E) 24 volts

70) A galvanometer having an armature coil with a resistance of 10 ohms requires 0.01 amps for a full scale deflection. To convert this galvanometer to a voltmeter which will give a full scale deflection when the voltage is 120 volts, a coil in series must be added that will have a resistance in ohms of:

A) 40…..B) 120…..C) 1,200……D) 1,210……E) 11,900

71) It is known from quantum mechanics that a particle in a one dimensional potential well (such as shown in the diagram) can exist in a number of energy states. Imagine an electron confined between the boundaries x and x +  Dx, where Dx is 0.5 Angstroms.

Approximately, what is the uncertainty in the x-component of the  momentum of the electron ?

72) If DP x  is the uncertainty in the x –component of the momentum of the  electron, what is the uncertainty in the y-component of the momentum of the electron ?

73) Consider a free particle confined between two impenetrable walls at x and x + L.  What is the probability according to classical physics that the particle will be found between x and x + L/3 if no other information is given?

74) What is the probability according to quantum mechanics that the particle in its lowest energy state will be found between x and x + L/3?

75) What is the probability according to quantum mechanics that the particle in the second lowest energy state will be found between x and x + L/3?