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Physics >> Mechanics part 1 >> Kinematics Medical Exam

A ball is thrown up with some velocity after time t second it is at height h from the ground which is given by h = at -1/2 bt2. The dh/dt is zero at t equal to

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Joshi sir comment

dh/dt = a - bt 

so for dh/dt = 0 

t = a/b

Physics >> Mechanics part 1 >> Kinematics Medical Exam

A ball is thrown up with velocity 20m/s relative to ground in open lift moving up with speed 10m/s at time of throwing and has an acceleration of 2 m/s upward, ball meets lift after     

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Joshi sir comment

relative to lift 

u of the ball = 20-10 = 10

a = 10-(-2) = 12 downward

and s = 0 because ball returns to initial point 

now use s = ut + 1/2 a t2

 

Physics >> Mechanics part 1 >> Kinematics Medical Exam

Velocity of a particle is given by v= 3-t m/s. The distance travelled by particle in 1st four second is

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Joshi sir comment

04 |v|dt  = 0(3-t)dt + 34(t-3)dt

now solve 

Physics >> Mechanics part 1 >> Kinematics Medical Exam

A bus is begins to move with an acceleration of 1 m/s2. A boy who is 48 m behind the bus starts running  at 10 m/s towards the bus. After what time bus will cross the boy?

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Joshi sir comment

according to the given condition 

1/2 t2+ 48 = 10t

solutions of this eq. = 12, 8

so boy will cross the bus after 8 sec and then bus will cross the boy after 12 sec from start.

Physics >> Mechanics part 1 >> Kinematics Medical Exam

 

The acceleration of a particle, varies with time according to the relation                     a=-mw2sinwt.The displacement of this particle at a time t will be

1) m sin(wt)

2) mwcos(wt)

3) mwsin(wt)

4) -1/2(mw2sinwt)t2

 

 

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Joshi sir comment

a = dv/dt = -mw2sinwt

so   ∫dv = -mw2sinwtdt

so v = mwcoswt + C

at t=0, v=0 so 0 = mw+C or C = -mw

so v = -mw(1-coswt)

similarly put v = ds/dt and integrate again 

Physics >> Mechanics part 1 >> Kinematics Medical Exam

A motor boat going down stream ,overtakes a floating object in water .One hour later ,the motor boat turned back .If speed of motor boat in still water is constant and flow velocity is also assumed constant,motor boat will again pass the floating object after time 't ' given by

1)Greater than 2 hrs

2)Equal to 2 hrs

3)less than 2 hrs

4)less than 1 hr

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Joshi sir comment

see video in you tube under the name iitbrain

video i e irodov 1.1 

time will be 1 hour

Physics >> Mechanics part 1 >> Kinematics Medical Exam

A paper weight is dropped from the roof of a 35 storey building each storey being 3m high. It passes the ceiling of the 20th storey at x m/s [g=10 m/s2]. Find x.

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Joshi sir comment

total height = (35-20+1)*3 = 48 m

now solve

Physics >> Mechanics part 1 >> Kinematics Medical Exam

A lift with open top is moving up with acceleration f. A body is thrown up with speed u relative to lift and it comes back to lift in time t. Then speed u is ...

{g = acceleration due to gravity}

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Joshi sir comment

relative acc. = g+f

and relative velocity = u

now solve

Physics >> Mechanics part 1 >> Kinematics Medical Exam

A projectile is thrown with speed 40 ms-1 at angle θ from horizontal. It is found that projectile as at same height at 1s and 3s. What is the angle of projection?

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Joshi sir comment

It is found that projectile as at same height at 1s and 3s, so half time of flight = 2 sec 

now solve

Physics >> Mechanics part 1 >> Kinematics Medical Exam

A particle is thrown with a velocity of u m/s. It passes A and B at time t1 = 1s  and t2 = 3s. The value of u is (g=10 m/s2).

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Joshi sir comment

question is not complete

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