1ei 55 ta ke nie naa amar bhalo mato doubt achhe...
eta kono ekbar iit te esechhilo ...
34 . A strip of wood of length l is placed on a smooth horizontal surface . An insect starts from one end of the strip , walks with a constant velocity and reaches the other end in time t1 . it then flies off vertically . The strip moves a further distance l in time t2.
a>t2=t1 b>t2<t1 c>t2>t1
d>either b or c depending on the masses of the insect or the strip .
55 . A particle moves along the x-axis as follows : it starts from rest at t=0 from a point x=0 and comes to rest at t=1 at point x=1 . No other information is available about its motion for the intermediate time (0<t<1) . If α denotes the instanttaneous accleartion of the particle then
a> α cannot remain positive for t in the interval 0≤t≤1 .
b> mod α cannot exceed 2 at any point in its path .
c> mod α must be ≥ 4 at some point or points in the path
d> α must change sign during the motion , but no other assertion can be made with the information given
61. Two particles A and B start simultaneously from the same point and move in a horizontal plane . A has innial velocity u1 due east and acceleartion a1 due north . B has innitial velocity u2 due north and acceleration a2 due east .
a> Thier path must intersect
b> They must collide at some point
c> They will collide only if u1a1=a2u2
d> If u1>u2 and a1>a2 , the particles will have the same speed at some point of time
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6 Answers
1
1at any point of time 't',
x1 = u1 t , y1= 1/2a1t2
y2= u2 t , x2= 1/2 a2 t2
now if they collide, at that time 't', then,
x1=x2 => t=2 u1/ a2
also, y1=y2 => t= 2u2/ a1
both time are same.. so u1/a2= u2/a1 => a1u1 = a2u2.
now, velocities at any point of time:
V1 = √u12 + (a1t)2
v2 = √u2 2 +(a2t)2
if If u1>u2 and a1>a2 , then v1=v2 at some point of time..
finally option A is obvious! think abt the trajectory...
10655. a,b it cant be d because we can make other assertions from the given information....
134.) let mass of cheeti =m and vel of cheeti : v
again let mass of wood = M
then, no extrenal force, so conservation of mom..
so, vel of lakdi : mv/(m+M) = v' (say) obviously < v
now, t1 = L/v
and t2 = L/v'
v'< v => t2>t1