NAROK UNIVERSITY COLLEGE
SPECIAL/SUPPLEMENTARY UNIVERSITY EXAMINATIONS 2010/11
UNIVERSITY EXAMINATIONS FOR THE DEGREE OF BACHELOR OF SCIENCE
(COMPUTER), BACHELOR OF SCIENCE AND BACHELOR OF EDUCATION (SCIENCE)
PHY110:
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BASIC PHYSICS I
Date: ___NOV 2010_______________________
Time: ______________
INSTRUCTIONS:
Answer Question ONE and any other THREE.
Use of sketch diagrams where necessary and brief illustrations are encouraged. Read the
instructions on the answer booklet keenly and adhere to them.
PHYSICAL CONSTANTS
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Acceleration due to gravity, g = 9.81ms-2
Universal gas constant R = 8.314 Jmol-1K-1
Avogadros number NA = 6.023x1023particles per mol
Boltzmann constant KB =1.381x10-23JK-1
Specific heat capacity of water cW =4186 Jkg-1K-1
Specific heat at constant pressure for Hydrogen, cP =28.8J//mol.K
Specific heat at constant volume for Hydrogen, cV =20.4J//mol.K
Speed of sound in air v = 343 m/s
Density of air = 1.20kg/m3
Specific heat capacity of copper ccu = 0.092 cal/g.oC
Latent heat of vaporization of Nitrogen Lvap= 48cal/g
Universal Gravitational Constant; G = 6.673x10-11Nm2kg-2
Stefan’s constant = 5.669 x 10-8Wm-2K-4
QUESTION ONE: [24 marks]
a)
A book is moved once around the perimeter of a tabletop with the dimensions 1.0 m x 2.0 m. If
the book ends up at its initial position, what is its displacement? What is the distance traveled?
[2]
b) If the component of vector A along the direction of vector B is zero, what can you conclude
about the two vectors? [1]
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c) State which of the following quantities, if any, remain constant as a projectile moves through its
parabolic trajectory: [3]
(i)
speed,
(ii)
acceleration,
(iii)
horizontal component of velocity,
(iv)
vertical component of velocity.
d) Suppose a truck loaded with sand accelerates along a highway. If the driving force on the truck
remains constant, what happens to the truck’s acceleration if its trailer leaks sand at a constant
rate through a hole in its bottom? [2]
e) Explain why the Earth is not spherical in shape and bulges at the equator. [2]
f) Can the average power over a time interval ever be equal to the instantaneous power at an
instant within the interval? Explain. [2]
g) An object of mass m starts from rest and slides a distance d down a frictionless incline of angle
q. While sliding, it contacts an unstressed spring of negligible mass as shown in figure 1. The
object slides an additional distance x as it is brought momentarily to rest by compression of the
spring (of force constant k). Find the initial separation d between object and spring. [2]
Figure 1
h) If two particles have equal kinetic energies, are their momenta necessarily equal? Explain. [2]
i) Smoke rises in a chimney faster when a breeze is blowing. Use the Bernoulli effect to explain
this phenomenon. [1]
j) How can an object move with respect to an observer so that the sound from it is not shifted in
frequency? [2]
k) What does the ideal gas law predict about the volume of a sample of gas at absolute zero? Why
is this prediction incorrect? [1]
l) A 1.00-mol sample of hydrogen gas is heated at constant pressure from 300 K to 420 K.
Calculate
(i)
the energy transferred to the gas by heat [2],
(ii)
the increase in its internal energy, [1] and
(iii)
the work done on the gas. [1]
QUESTION TWO: [12 marks]
a)
The center of gravity of an object may be located outside the object. Give three examples for
which this is the case. [3]
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b)
Figure 2 shows three uniform objects: a rod, a right triangle, and a square. Their masses and
their coordinates in meters are given. Determine the center of gravity for the three-object system
[5]
Figure 2
c) A vaulter holds a 29.4-N pole in equilibrium by exerting an upward force U with her leading
hand and a downward force D with her trailing hand, as shown in Figure 3. Point C is the
center of gravity of the pole. What are the magnitudes of U and D? [4]
Figure 3
QUESTION THREE: [12 marks]
a) What is a major problem that arises in measuring specific heats if a sample with a temperature
above 100°C is placed in water? [3]
b) A water heater is operated by solar power. If the solar collector has an area of 6.00 m2 and the
intensity delivered by sunlight is 550 W/m2, how long does it take to increase the temperature of
1.00 m3 of water from 20.0°C to 60.0°C? [5]
c) A 1.00-kg block of copper at 20.0°C is dropped into a large vessel of liquid nitrogen at 77.3 K.
How many kilograms of nitrogen boil away by the time the copper reaches 77.3 K? (The
specific heat of copper is 0.092 0 cal/g . °C. The latent heat of vaporization of nitrogen is 48.0
cal/g.) [4]
QUESTION FOUR: [12 marks]
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a) Suppose the wind blows. Does this cause a Doppler effect for sound propagating through the air?
Do you treat this as a moving source or a moving observer? [3]
b) A sound wave in air has pressure amplitude equal to 4.00 x 10-3 N/m2. Calculate the displacement
amplitude of the wave at a frequency of 10.0 kHz [4]
c) The area of a typical eardrum is about 5.00 x 10-5 m2. Calculate the sound power incident on an
eardrum at
(i) the threshold of hearing and
(ii) the threshold of pain. (Take intensity at the threshold hearing = 1.0 x 10-12 W/m2 and
threshold pain = 1.0 W/m2) [5]
QUESTION FIVE:
[12 marks]
a) Describe how a driver can steer a car traveling at constant speed so that (a) the acceleration is
zero or (b) the magnitude of the acceleration remains constant. [4]
b) The vector position of a particle varies in time according to the expression r = (3.00i - 6.00t2j)
m.
(i) Find expressions for the velocity and acceleration as functions of time. [2]
(ii) Determine the particle’s position and velocity at t =1.00 s [2]
c) A firefighter, a distance d from a burning building, directs a stream of water from a fire hose at
angle q above the horizontal as in figure 4. If the initial speed of the stream is vi, at what height
h does the water strike the building? [4]
Figure 4
QUESTION SIX:
[12 marks]
a) Ethyl alcohol has about half the specific heat of water. If equal-mass samples of alcohol and
water in separate beakers are supplied with the same amount of energy, compare the
temperature increases of the two liquids [2]
b) A box with a total surface area of 1.20 m2 and a wall thickness of 4.00 cm is made of an
insulating material. A 10.0-W electric heater inside the box maintains the inside temperature
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at 15.0°C above the outside temperature. Find the thermal conductivity k of the insulating
material. [5]
c) The tungsten filament of a certain 100-W light bulb radiates 2.00 W of light. (The other 98 W is
carried away by convection and conduction.) The filament has a surface area of 0.250 mm2 and
an emissivity of 0.950. Find the filament’s temperature. (The melting point of tungsten is 3 683
K.) [5]
End and Good Luck.
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