1 )
A boat which has speed of 5 km / h in still water across a river of width of
1km along the shortest path in 15 minutes . The velocity of river in km /
s is : -
A ) 3 km / h , B ) 7 km / h
,
C ) 18 km / h , D ) 21 km / h ,
Correct
Answer : - A ) 3 km / h
,
Solution
: -
Let the velocity of river be ‘x’ km
/ hr .
Speed of boat
= 5 km / h , And
Width of river ( AB )
= 1 km / hr .
Time taken to cross the river by boat = 15
minutes .
So distance covered by boat : -
d = v t ,
d = 5 x 15 / 60
= 1.25 km / hr .
Now , AB = 1 km / hr ,
And AC = 1.25 km / hr .
And angle β = 90°
.
So ,
( AB ) ^ 2 + ( BC ) ^ 2
= ( AC ) ^ 2 ,
1 + ( BC ) ^ 2
= ( 1.25 ) ^ 2 ,
So , BC =
0.75 km .
So , distance covered by river water in 15 minutes
is 0.75 km / hr .
Velocity of river : -
v = d / t
= 0.75 / (1/4) ,
v =
3 km / h ,
Answer .
2 ) The velocity time graph of a car is moving along a straight road is shown in figure . The average velocity of car in first 25 seconds is : -
Choose
single option from these following : -
A ) 5 m / s , B
) 10 m / s ,
C ) 14 m / s , D ) None of these ,
Correct
Answer : - C ) 14 m / s ,
Solution : -
3 )
The velocity – time graph for particle is moving in a straight line . The sum
of two shaved areas represents : -
A ) increase in displacement of a particle ,
B ) the average velocity of a particle ,
C ) average acceleration of particle ,
D ) the distance moved by a particle ,
Correct Answer : - D ) the distance moved by a particle ,
Solution : -
