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. September 2016

Momentum of a laser pulse

Q- A pulsed laser fires a 1000-MW pulse horizontally at a 10mg mass suspended vertically from a 4 cm long fiber of negligible mass. If the pulse lasts duration of 200 nanoseconds, and the radiation is completely absorbed by the mass, by what maximum angle is the pendulum deflected?

Solution:

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Alternating current: Impedance

Q- A series combination of R = 1000Ω, L = 500 mH and C = 150µF is connected to a sinusoidal voltage supply of frequency 50Hz. The circuit has a peak amplitude of 1A. Calculate the voltage amplitude of the supply generator.

Solution:

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Simple Harmonic Motion

A block attached to a spring with unknown spring constant oscillates with a period of 3.0 s.

(a) What is the period if the mass is doubled?

(b) What is the period if the mass is halved?

(c) What is the period if the amplitude is doubled?

(d) What is the period if the spring constant is doubled?

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Electromagnetic Induction: Faraday's law

Q- A coil of area 0.1m2 is rotating at 60rev/s. with its axis of rotation perpendicular to a 0.2T uniform magnetic field.

(a) If the coil has 1000 turns, what is the maximum EMF generated in it?

(b) What is the orientation of the coil with respect to the magnetic field when the maximum induced vol…

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Motion under gravity

(On request- Nick)

Q- A ball is thrown straight up at a speed of 20m/s. On its way down, the ball is caught 5m above from where it was thrown. 
a. How fast is the ball moving when it is caught? 
b. How long is the ball in the air? 

Solution:

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Standing Waves on String

Q- The G string on an instrument is 49 cm long. When played without fingering, it vibrates at a frequency of 196 Hz. The next higher notes on the C-major scale are A (220 Hz), B (247 Hz), C (262 Hz), and D (294 Hz). What distance x from the end of the string must a finger be placed to play each of t…

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Electrostatics: Field

Q- Consider the rectangle below BCDE of length 24cm. and width 18cm. Position A is at the center of the rectangle. Point charges q1 = (+) 0.2 µC, q2 = (+) 0.8 µC and q3 = (-) 0.6 µC are placed at the corners B, C and D of the rectangle as shown. Find the magnitude and direction of the electric fie…

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Fluid: Pressure

Q- A side door near the bottom of an oil tank is shown in the figure. Find the force on the door due to the oil pressure. The density of the oil is 855 kg/m3.

Solution:

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Electric charge in a magnetic field

Q- Positively and negatively charged particles are simultaneously “shot” with velocity v through the magnetic field B as in figure, in the plane of the paper. Find the magnitude and direction of the force acting on each particle.

Solution:

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Friction

Q- A block of weight 125 N is placed on a horizontal surface and subjected to a force of 75 N as shown in the figure.

(a) If the block remains stationary, find the force of friction acting on the block.

(b) If the block is at the verge of sliding find the coefficient of static friction.

Solutio…

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Electromagnetic Induction.

Q- A 25 turn circular coil of wire has a diameter of 1.0m. It is placed with its axis (a line through the center of the coil at right angles to its plane) along the direction of the Earth’s magnetic field of 50 µT. The coil is then flipped in a time of 0.2s through an angle of 1800. Calculate the…

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Projectile Motion

Q- In the javelin throw at a track-and-field event, the javelin is launched at a speed of 40.0 m/s at an angle of 37° above the horizontal. As the javelin travels upward, its velocity points above the horizontal at an angle that decreases as time passes. How much time is required for the angle to be…

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Alternating current

Q- A 100 µF capacitor is connected in turn to two different sinusoidal voltages of the same amplitude V = 1.0V but different frequencies with f1 = 50Hz and f2 = 5kHz.

(a) Calculate the reactance X1 and X2

(b) By what factor is X1 greater than X2 ?

(c) Calculate the amplitudes of the associated c…

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Torque

Q- (a) Calculate the force required in the deltoid muscle (Fm) to hold up the outstretched arm as shown in the figure. The mass of the arm is 2.8 kg.

(b) What is the muscle force and the reaction Fj at joint if the hand holds a ball of mass 5 kg at a distance 50 cm from the shoulder joint?  

So…

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Capacitance

Q- A commercial capacitor is to be constructed as shown in Figure. This particular capacitor is made from two strips of aluminum foil separated by a strip of paraffin-coated paper. Each strip of foil and paper is 7.90 cm wide. The foil is 0.00400 mm thick, and the paper is 0.0250 mm thick and has a …

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Roller Coaster

Q- A roller coaster car has a mass of 500kg when fully loaded with passengers. The radius of the coaster is 10m.

(a) If the vehicle has a speed of 20.0 m/s at the lowest point, what is the force exerted by the track on the car at this point?

(b) What is the maximum speed the vehicle at the hig…

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Current electricity: Resistance, Drift speed

Q- A solid cube of silver (density = 10.5 g/ cm3) has a mass of 90.0 g.

(a) What is the resistance between opposite faces of the cube?

(b) Assuming each silver atom contributes one conduction electron, find the average drift speed of electrons when a potential difference of 1.00*1O-5V is applied t…

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Fluids: Viscous Drag

Q- Calculate the force required to pull a copper ball of radius 2.00cm upward through a fluid at the constant speed 9.00 cm/s. Take the drag force to be proportional to the speed, with proportionality constant 0.950 kg/s. Ignore the buoyant force.

Solution:

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Electrostatics: Field and Potential

Q- Given two 2.00-mC charges, as shown in Figure and a positive test charge q = 1.28*10-18 C at the origin,

(a) What is the net force exerted by the two 2.00-mC charges on the test charge q?

(b) What is the electric field at the origin due to the two 2.00mC charges?

(c) What is the electri…

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Simple Harmonic Motion

Q- A block with mass M attached to a horizontal spring with force constant k is moving with simple harmonic motion having an amplitude A . At the instant when the block passes through its equilibrium position, a lump of putty with mass m is dropped vertically onto the block from a very small height …

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