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Physicshelpline

. October 2016

Heat Engine

(On request Dyllzey)

Q- A gas is taken through the cycle as shown in the figure. Find

(a) Change in internal energy of the gas during one cycle  

(b) Work done on the gas during one cycle

(c) Net heat transferred to the gas during one cycle

Solution:

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Magnetic Field: Parallel Wires

Q- Two long parallel horizontal wires are interacting to each other by a force per unit length of 320 micro-newton/meter, when they are separated by a vertical distance of 0.500m. The current in the upper wire is 20.0 A to the right. Determine the location of the line in the plane of the two wires a…

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Simple Harmonic Motion

Q- 240 g mass on a 0.8 m long string is pulled 8.4° to one side from its equilibrium position and released. How long does it take for the pendulum to reach 6.0° on the opposite side?

Solution:

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Modern Physics: Relativity

Q- A certain star is 18.6 light years away. How long would it take a space craft traveling at 0.950c to reach that star from earth as observed (a) on earth (b) on the spacecraft.

Solution:

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Newtons Laws of motion: Friction

Q- A loaded penguin sled weighing 90 N rests on a plane inclined at angle θ = 30° to the horizontal. Between the sled and the plane, the coefficient of static friction is 0.27 and the coefficient of kinetic friction is 0.20.

(a) What is the minimum magnitude of the force F, parallel to the plane,…

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Electrostatics: Field

Q- An isolated charged conducting sphere of radius 15.0 cm creates an electric field of 4.90*104 N/C at a distance 22.0 cm from its center.

(a) What is its surface charge density?
(b) What is its capacitance?

Solution:

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Thermal Physics: Gas Law

Q- A cylinder of hydrogen, 2m in height and with a 25cm diameter, is dropped and develops a crack of size 0.1 mm2. The gas is stored at 10 bar absolute pressure. Estimate how long it takes for half the contents to leak out. Explain your reasoning and assumptions.

Solution:

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Alternating current

Q- An alternating waveform is given by the voltage as a function of time as

             V(t) = 3 cos (2t) + 4 sin (2t)

Calculate the peak voltage, rms voltage and the phase at t = 0.

Solution:
 

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Dimensional Analysis

Q- The thickness h of a puddle of water on a waxy surface depends on the density ρ of the liquid, the surface tension γ (SI units: N/m) and acceleration due to gravity g. Use dimensional analysis to find a relationship between the thickness and the other 3 variables.

Solution:

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Electromagnetic Induction: Transformer

Q- A step-down transformer is used for recharging the batteries of portable devices. The turns ratio inside the transformer is 13:1 and it is used with 120-V (rms) household service. If particular ideal transformer draws 0.350 A from the house outlet, what are

(a) The voltage

(b) The current suppl…

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Newtons Laws of motion

(On request)

Q- Two masses m1 = 8.00 kg and m2 = 12.0 kg, connected be a massless string are placed on a triangular wedge of inclines θ1, and θ2 as in the figure. (friction is negligible)

(a) Find the acceleration of the masses.

(b) Find tension in the string.

Solution:

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Electromagnetic Induction: Faraday's law

Q- A coil consists of 200 turns. Each turn is a square of wire of side 18cm. A magnetic field produced by an electro-magnet and directed perpendicular to the plane of the coil is switched on. If the field changes linearly from 0 to 0.5T in 0.8s:

(a) What is the induced emf in the coil while the fie…

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Current electricity: Resistance and Capacitor

Q- Consider the circuit bellow remains connected for long time.

(a) Calculate the voltage across the capacitor.  

(b) Calculate the current through the resistances.

(c) Calculate the charge on the capacitor.

Solution:

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Bohr Model

Q- In the Bohr model of the hydrogen atom, the speed of the electron is approximately 2.20 X 106 m/s. Find

(a) The force acting on the electron as it revolves in a circular orbit of radius 0.530 X 10-10 m and

(b) The centripetal acceleration of the electron.

Solution:

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Simple Harmonic Motion

Q. A 170 g mass attached to a horizontal spring oscillates at a frequency of 2.0 Hz. At t = 0 s, the mass is at x = 5.0 cm and has vx = -28 cm/s. Determine the following.

(a) The period  (b) The angular frequency  (c) The amplitude  (d) The phase constant  (e) The maximum speed  (f) The maximum acc…

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Magnetic Field: Parallel Wires

Q- Two long parallel conductors, separated by 10.0 cm, carry currents in the same direction. The first wire carries current I1 = 5.00A and the second one carries I2 = 8.00A.

a) What is the magnitude of the magnetic field created by I1 at the location of I2?

b) What is the force per unit length exe…

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Interference (sound)

Q- Two loudspeakers emit sound waves along the x-axis. The sound has maximum intensity when the speakers are 22 cm apart. The sound intensity decreases as the distance between the speakers is increased, reaching zero at a separation of 66 cm.

(a) What is the wavelength of the sound?
(b) If the d…

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Electrostatics: Field

Q- Three point charges are aligned along the x axis as shown in Figure. Find the electric field at

(a) The position (2.00m, 0)

(b) The position (0, 2.00m).

Solution:

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Newtons Laws of motion: Variable mass

Q- A boat of mass 250kg is coasting, with its engine in neutral, through the water at speed 3.00m/s when it starts to rain. The rain is falling vertically, and it accumulates in the boat at the rate of 10.0 kg/hr.What is the speed of the boat after time 2.00hr has passed? Assume that the water is st…

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Charging of a capacitor

Q- A capacitor in an RC circuit is charged to 60.0% of its maximum value in 0.900 s. What is the time constant of the circuit?

Solution:

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