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. July 2017

Modern Physics: Absorption of Gamma Rays

Q- A collimated gamma ray beam consists of equal numbers of 0.1 MeV and 1.0 MeV photons. If the beam enters a 15 cm thick concrete shield, what is the relative portion of 1 MeV photons to 0.1 MeV photons in the emergent beam? 

Solution:

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Rotational Motion

Q- A steel shaft (density = 8050 kg/m3) is 2m long and is accelerated from rest to 400 rpm in 6 seconds by a torque of 100 Nm. Determine the diameter of the shaft.

Solution:

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Electromagnetic waves

Q- The intensity of sunlight striking the earth's upper atmosphere (called the solar constant) is 1.35 kW/m2.

(a) Find Erms and Brms due to the sun at the upper atmosphere of the earth.

(b) Find the average power output of the sun

(c) Find the intensity at the surface of the sun. 

(d) Find th…

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Friction and Projectile

Q- A block slides 6 feet down the incline of an escalator and then it slides for 2 feet along the level portion until if flies off. If the level portion of the escalator is 3 feet above the floor, determine how far from the base of the escalator the block will strike the floor. Assume that the coeff…

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Magnetic Flux

Q- Find the total flux linkage of the coil shown in figure if each flux line represents 2*10-7 Wb.

(a)What is the equivalent flux linking all of the turns in Figure?

(b) What is the flux linking per turn?

Solution:

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Heat and Thermodynamics

Q- A spherical tank contains 1 mole of helium gas at 10 bar and 300 K. The gas is slowly released to the atmosphere in such a way the remaining gas is maintained at constant total energy U. Heating or cooling may be used to keep U constant during the venting. Helium behaves as an ideal gas with a co…

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Electrostatics: Field in Cavity

Q. A sphere of radius r0 carries a volume charge density ρE. A spherical cavity of radius r0/2 is then scooped out and left empty, as shown. 

(a) What is the magnitude and direction of the electric field at point A? 

(b) What is the direction and magnitude of the electric field at point B? Poin…

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Elasticity: Torque and Twist

Q- The torques shown are exerted on the pulleys A, B, and C. Knowing that both shafts are solid and made of brass (G = 39GPA), determine the angle of twist between (a) A and B, (b) B and C.

Solution:

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Fluid Dynamics

Q- A hypodermic syringe is attached to a needle that has an inner radius of 0.305 mm and a length of 3.00 cm. The needle is field with a solution of viscosity 2.01*10-3 Pa.s. It is injected in to a vein at a gauge pressure of 16.6 mm of Hg.

(a) What must the pressure of the fluid in the syringe be …

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Alternating Current: Series Resonance

The cut-off frequencies of a series resonant circuit are 5400 Hz and 6000 Hz.

(a) Find the Bandwidth of the circuit.

(b) If  quality factor Q = 9.5, find the resonant frequency of the circuit.

(c) If the resistance of the circuit is 2 Ω, find the value of reactance  XL and XC at resonance…

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Sound Waves: Interference

Q- A riverside warehouse has two open doors and its walls are lined with sound absorbing material. A boat on the river sounds its horn. To a person A on the perpendicular bisector of the doors, at a distance 150 m from the doors, sound is loud and clear while to a person B, 30 m sideways from A, the…

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Force and Friction

(On request- William)

Q- is it easier to move a box that is sitting on the ground (a) by pulling the box from a rope that makes an angle of 300 with the surface or(b) by pushing the box with the force that makes the same angle (but pointing downward) with the surface?

Solution:

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Photo Electric Effect

Q- An ultraviolet photon with wavelength 172 nm strikes an aluminum surface with a work function φ = 3.87 eV and ejects an electron. What is the shortest wavelength λ that can be observed for the ejected electron?

Solution:

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NLM: Tension

(On request- William)

Q- A traffic light weighing 122N hangs from a cable tied to two other cables fastened to a support. The upper cables make angles 370 and 530 with the horizontal. Find the tension in the cables.

Solution: 

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Ray Optics: Total Internal Reflection

Q- A layer of unknown liquid is held on a flint glass slab with an index of refraction 1.65. A ray of light is falling on the glass liquid interface from below and the critical angle for the interface is 530.

(a) What is the refractive index of the unknown liquid?

(b) If the liquid is removed, wha…

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Work Power Energy: Conservation of Energy

Q- A particle of mass m=5.00 kg is released from point A and slides on the frictionless track. Determine

(a) the particle's speed at points B and C. and

(b) the net work done by the gravitational force as the particle moves from A to C. 

Solution:

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