575 - Physics Questions Answers

Can You Please Explain the Cartesian method for mirror and Lens?

Asked By: BONEY HAVELIWALA
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Joshi sir comment

Cartesian method is the method of sign convention

Sign Convention for Spherical Mirrors and Thin Lenses 
 
 
                                   Spherical Mirrors                   Lenses 
Focal Length            - for concave mirrors            + for a converging lens  
                              + for convex mirrors               - for a diverging lens 
Object Distance           - real object                     - real object 
                                + virtual object                 + virtual object
 
 
Image Distance           - real image                          + real image 
                                 + virtual image                   - virtual image 
Magnification            + for erect image                 + for erect image  
                              - for inverted image            - for inverted image 

Sir/Madam, 

                    Can you please explain me to find potential difference between two plates of capacitor like this shown in figure. Can you Give anymore examples if possible? Thank You! (Please omit time)

Asked By: BONEY HAVELIWALA
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Joshi sir comment

after time t charge on plates of capacitor q = CE(1-e-t/RC) 

then potential difference between the plates of capacitor = q/C

after a long time this potential difference = E      [this can be obtained by putting t = ∞]

A particle has initial velocity of y = 3i+ 4j and a constant force F = 4i -3j acts on it. Then what will be the path followed by the particle?

Asked By: VIKRAM
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Joshi sir comment

acceleration is constant and initial velocity is perpendicular to it because dot product of two given vectors is 0 so this is the case equivalent to a particle thriwn from the top of a building horizontally under gravity so path will be parabolic

if you want the equation of path then reply

A block of mass 100 g is moved with a speed of 5 m/s at the highest point in a closed circular tube of radius 10 cm kept in vrtical plane.The cross section of the tube is such that the block just fits in it.The block makes several oscillations inside the tube and finally stops at the lowest point. Find the work done by the tube on the block.

Asked By: SUBHASH
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Joshi sir comment

Total energy is lost so K E will be the work done

A ball is dropped from the top of the tower of height h. It covers a distance h/2 in the last second of its motion. How long does the ball remain in air?

Asked By: GAUTAM SAGAR
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Joshi sir comment

let total time of flight = t

so h = gt2/2 and

h/2 = gt-(g/2)

so gt2/4 = gt-(g/2)

or t2/4 = t -(1/2)

now solve 

Physics >> Mechanics Part 2 >> Gravitation Medical Exam

If L is the angular momentum of a satellite revolving around earth is a circular orbit of radius r with speed v, then (i) L α v

(ii) L α r

(iii) L α √v

(iv) L α √r

Asked By: SWATI KAPOOR
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Joshi sir comment

L = m*v*r

 

Physics >> Mechanics Part 2 >> Gravitation Medical Exam

If potential energy of a body of mass m on the surface of earth is taken as zero then its potential energy at height h above the surface of earth is [ R is radius of earth and M is mass of earth]

Asked By: SWATI KAPOOR
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Joshi sir comment

[-GMm/(R+h)]-[-GMm/R] = GMm[1/R - 1/(R+h)]

solve ?

Physics >> Mechanics Part 2 >> Gravitation Medical Exam

Two points masses having m and 4m are placed at distance at r. The gravitational potential at a point, where gravitational field intensity zero is

Asked By: SWATI KAPOOR
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Joshi sir comment

field intensity at distance x from m = Gm/x2 - G4m/(r-x)2

compare it to 0 and find x

then calculate gravitational potential at the point 

Physics >> Mechanics Part 2 >> Gravitation Medical Exam

During motion of a planet from perihelion to aphelion the work done by gravitational force of sun on it is positive or negative.

Asked By: SWATI KAPOOR
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Joshi sir comment

change in K E = work done by all the forces

and from perihelion to aphelion velocity decreases

so work done will be negative

Physics >> Mechanics Part 2 >> Gravitation Medical Exam

If an object is projected vertically upwards with speed, half the escape speed of earth , then the maximum height attained by it is [R is radius of earth]

Asked By: SWATI KAPOOR
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Joshi sir comment

from ground to that point 

1/2 m[√(2gR)/2] + [-GMm/R]  =  0 + [-GMm/(R+h)]

solve for h

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