575 - Physics Questions Answers

The acceleration (a) of a body moving along x-axis is given by a=4x3 ,where a is in m/s2 and x is in metre.if at x=0 the velocity of body is 2m/s,then find its velocity at x=4m?

Asked By: AVANTIKA PURI
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Joshi sir comment

a = 4x3

so dv/dt = 4x3

or dv/dx * dx/dt = 4x3

or dv/dx * v = 4x3

or vdv = 4x3dx

or ∫vdv = 4∫x3dx

or v2/2 = 4x4/4 + C

at x = 0, v = 2

so 4/2 = 0+C

so C = 2

on putting the value of C

we get v2/2 = x4+ C

now put x = 4 and get v

The position x of a particle moving along x-axis at time t is given by equation t=√x +4 , where x is in meter and t is in seconds. Find the position of particle when its velocity is zero.

Asked By: AVANTIKA PURI
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Joshi sir comment

given that x = (t-4)2

so dx/dt = 2(t-4) 

or v = 2t-8

now for v=0, t=4

put t=4 and get x

Physics >> Mechanics part 1 >> Kinematics Medical Exam

A body projected upwards is at same height form ground at t=3s and t=7s . Find the maximum height attained by it. ( take g= 10 m/s^2 ).

Asked By: AVANTIKA PURI
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Joshi sir comment

A body projected upwards is at same height form ground at t=3s and t=7s. It will gain max. height after 5 second

so maximum height = gt2/2 = 10*5*5/2 = 125 

another direct method for finding total distance = 5+15+25+35+45 = 125

these are the distances in 1st, 2nd, 3rd and etc sec. 

What would be the Potential energy of two points charges q &-q which r separated by a dist d  ( IF POTENTIAL AT MID PT IS TAKEN TO BE ZERO)

 

Asked By: SARIKA SHARMA
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Joshi sir comment

potential energy = -kqq/d

Physics >> Mechanics part 1 >> Kinematics Medical Exam

a particle , with an inital velocity v0 in a plane , is subjected to a constant acceleration in the same plane . then in general ,

the path of the particle would be

1) circle

2) ellipse

3) parabola

4)   hyperbola

Asked By: SARIKA SHARMA
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Joshi sir comment

parabola 

for understanding this make components of v parallel and perpendicular to a

Physics >> Mechanics part 1 >> Kinematics Medical Exam

a train is moving with a velocity of 30m/s. When brakes are applied , it is found that the velocity  reduces to 10m/s in 240m.

When the velocity of the train becomes zero , the total distance travelled is??

270m   

Asked By: SARIKA SHARMA
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Joshi sir comment

by v2 = u2-2as

100 = 900-2*a*240

or 800 = 480a

or a = 80/48 = 10/6 = 5/3

so total distance upto rest is u2/2a = 900*3/2*5 = 270m

A CARNOT ENGINE WORKING B/W 270 C & --1230C HAS EFFICIENCY η . IF TEMP OF SINK IS DECREASED BY 50K THE EFFICIENCY BECOMES??

ANS  4η/3

Asked By: SARIKA
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Joshi sir comment

according to the given condition η = 1-(150/300) = 0.5

now after decreasing temperature of sink by 50K

we get the new efficiency = 1-(100/300) = 2/3 = 4*0.5/3 = 4η/3

in a thermodynamic process on 2 moles of a monoatomic gas work done on gas is 100J & change in temp is 30 C . The change in internal energy of the gas in this process is??

Asked By: SARIKA
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Joshi sir comment

change in internal energy = nCvdT = 2*[R/(γ-1)]*30 = 60*8.31/[(5/3)-1] 

while measuring the speed of sound by performing a resonance column expt , a student gets d first resonance conditn at a column length of 18 cm during winter . Repeating d same expt during summer , she measure d column length to be x cm for the second resonance. THEN

1)18>X

2)X>54

3) 54>X>36

4) 36>X>18

ANS (2)

AIEEE 2008

Asked By: SARIKA SHARMA
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Joshi sir comment

since l α λ α v/n          n is frequency

on increasing temperature, v increases so λ increases

for first resonance l = λ/4

and for third resonance L = 3λ'/4

and λ> λ so x will be more than 54  

 

Physics >> Mechanics part 1 >> Kinematics Medical Exam

angle b/w vectors (i^+j^)and(j^+k^)  is

1) 60o

2) 90o

3) 300

4) 450

Asked By: SARIKA SHARMA
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Joshi sir comment

use the formula A.B = |A||B|cosθ

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