575 - Physics Questions Answers

A bullet of mass m passes through a pendulum bob of mass M with velocity v and comes out of it with a velocity v/2. The minimum value of v so that tha bob mass complete one resolution in the vertical circle. (l= length of pendulum)

Asked By: SWATI KAPOOR
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Joshi sir comment

for completing revolution velocity of the bob at lowest point should be √5gl

so by momentum conservation mv = M√5gl + mv/2

now solve

A ball moving with speed v collides with a horizontal smooth surface at an angle ϴ with normal to surface. If coefficient of restitution is ‘e’ , then find velocity after rebounce making same angle theta with the normal.

 

 

Asked By: SWATI KAPOOR
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Joshi sir comment

let angle before collision is φ and after collision is θ with vertical then 

for vertical direction velocity after rebound = evcosφ

for horizontal direction velocity after rebound = vsinφ

now use pythagorus theorem 

If a particle is moving on a circular path with constant speed, then the angle between the direction of acceleration and its position vector wrt centre of circle will be

Asked By: SWATI KAPOOR
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Joshi sir comment

it should be 180 degree

 

Two blocks of masses 2 kg and 4 kg are hanging with the help of massless string passing over an ideal pulley inside an elevator. The elevator is moving upward with an acceleration g/2. The tension in the string connected between the blocks will be

Asked By: SWATI KAPOOR
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Joshi sir comment

equation 1

4g+4g/2-T = 4a

equation 2

T-2g-2g/2 = 2a

now solve

a particle starts with a constant tengential acceleration on a circle. the instant when it complete half circle what is the angle between its velocity vector and acceleration vector...???
Asked By: IMRAN AHMED
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Joshi sir comment

let tangential acc is a

then velocity after covering half circle 

v2 = 2a(πr)

so centripetal acc = v2/r = 2aπr/r = 2aπ

so angle = tan-1[2aπ/a] = tan-1

here notice that velocity will be in the direction of tangential acc.

is impedence as same as resistanace in a circuit // and // are capacitive reactance and inductive reactance constant values(i.e. independant of value of current in ac circuit at any time)  ?? 

Asked By: AAYUSH TANEJA
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Joshi sir comment

Write the question with correct symbols

 

yes it is equivalent to resistance for that circuit

For what angle should a body be projected with velocity 24m/s just to pass over the obstacle 16 m high at horizontal distance of 32 m? Take g=10 m/s^2

Asked By: RESHU SINGH
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Joshi sir comment

use the eq. 

y = xtanθ-(gx2/2u2cos2θ)

Physics >> Mechanics part 1 >> Kinematics Medical Exam

A rocket is fired vertically from the ground. It moves upward with a constant acceleration 10 m/s2 for 30s after which the fuel is consumed. After what time from the instant of firing the rocket will attain the maximum height?

Asked By: SWATI KAPOOR
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Joshi sir comment

total height covered in upward journey = at2/2 = 10*30*30/2 = 4500 = 4.5 km

after consuming all the fuel, it will fall with gravity and g = 10 m/sso it will move the same distance again upto stop

so max H = 9 km. 

Physics >> Mechanics part 1 >> Kinematics Medical Exam

a bullet is fired vertically upwards with an initial velocity of 50 m/s. It covers a distance h1 during the first second and a distance h2 during the last 3 seconds of its upward motion. If g = 10 m/s2, h1 and h2 will be related as

Asked By: SWATI KAPOOR
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Joshi sir comment

remember that gravity reduces velocity by 10 m/s on upward journey. 

Also understand the diagram given

 

Physics >> Mechanics part 1 >> Kinematics Medical Exam

a car is going eastwards with a velocity of 8m/s. To the passengers in the car , a train appears to be moving northwards with a velocity 15m/s. What is the actual velocity of the train?

Asked By: SWATI KAPOOR
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Joshi sir comment

vobserver = 8i

vtrain,observer = 15j

so by formula 

vtrain,observer = vtrain - vobserver

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