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Physicshelpline

. May 2017

Motion in 2D: Relative Velocity

Q1- Two particles 1 and 2 move with constant velocities v1 and v2. At the initial moment, their radius vectors are r1 and r2. How must these four vectors be interrelated for the particles to collide? 

Q2- A ship moving along the equator to the east with velocity v0 = 30 km/hr. The south-eastern wi…

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Gravitation: Orbital Speed

Q- A Star S have two planets A and B. Planet A has average orbital radius three times as big as planet B. If planet A orbits S in 2 earth years,

(a) How long is a year for the resident of planet B

(b) What is linear orbital speed of planet B, if the average radius of A is 3*1011 m. 

Solution:

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Ray Optics

Q- A fish is 10 cm from the front surface of a spherical fish bowl of radius 17 cm.

(a) How far behind the surface of the bowl does the fish appear to someone viewing the fish from in front of the bowl?

(b) By what distance does the fish's apparent location change (relative to the front surface o…

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Fluids: Archimedes' Principle

Q- A light balloon is filled with 400m3 of helium at zero degrees Celsius. What is the maximum mass of the payload the balloon can lift? 

Solution:

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Interference: Double Slit

Q- In a location where the speed of sound is 354 m/s, a 2000 Hz sound wave impinges on two slits 30.0 cm apart.

(a) At what angle with the perpendicular bisector of the slits is the first maximum located?   

(b) If the sound wave is replaced by a 3.00 cm microwave, what slit separation gives the…

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Standing Waves

Q- What are the three longest wavelengths for standing sound waves in a 121 cm long tube that is

(a) open at both ends

(b) Open at one end and closed at the other.

Solution:

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Electromagnetism

Q- An electron is moving straight towards a long straight wire with a velocity of 2*107 m/s. When the electron is 6 cm from the wire, a current I = 12 A suddenly appears in the wire. Find

(a) The magnitude and direction of the of the magnetic field of this current at the position of the electron.

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Rotational Motion

Q- A light cylindrical axle of radius r is free to rotate about its vertical axis. The upper end of the axle is attached to a light horizontal cross bar with two small masses, each M, at a distance R from the axle. A light string is wrapped on the axle and its free end is passing over a smooth light…

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Capacitors

Q- Two capacitors are connected to a battery with a two way swatch, as shown in figure. The capacitors are initially uncharged. When the switch is thrown to the left the capacitor C1 = 10 µF is charged to 50 V. Now the switch is thrown to the right and the voltage across C1 is drops to 35 V.

(a)…

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Friction

Q- An aluminum block is pushed to the right with and initial speed of v1=10 ft/s at the same time a copper block is pushed to the left with an initial speed of v2=16 ft/s. both blocks slide along a horizontal steel floor toward each other. if the blocks were initially d = 10 ft. apart determine how …

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Coulomb's Law: Force and Field

Q- Four charges q1 = q3 = - q and q2 = q4 = + q, where q = 7 µC, are fixed at the corners of a square with sides a = 2.2 m, as in figure.

(a) Calculate the x- and y-components of the net electric field at the midpoint M of the bottom side of the square.

(b) Find the total force exerted on q4 by…

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Gravitation

Q- A particle is projected from the surface of the earth with a speed twice of the escape speed.  Neglecting air resistance, find its speed when it is far away from the earth. 

Solution:

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Refraction at Curved Surfaces

Q- A goldfish lives in a 46 cm diameter spherical fish bowl. The fish sees a cat watching it. If the cat's face is 15 cm from the edge of the bowl, how far from the edge does the fish see it as being? (You can ignore the thin glass wall of the bowl.)

Solution:

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Kinematics: Motion in one dimension

(On request - Medhansh)

Q- A stone weighing 3kg falls from the top of a tower 100m high and buries itself 2m deep in the sand. What is the time of penetration.

Solution:

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14 .