Question

From a motorboat moving downstream with a velocity 2 m/s with respect to river, a stone is thrown. The stone
ralls on an ordinary boat at the instant when the motorboat collides with the ordinary boat. The velocity of the
ordinary boat with respect to the river is equal to zero. The river flow velocity is given to be 1 m/s. The initial
velocity vector of the stone with respect to earth is :-
Take the value of g - 10 m/s"
Initial separation between the two boats is 20m.
A) 21 +20
(B) 31 + 40j
(C) 31+ 50
(D) 21 + 50j
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Answer 1

Answer:

The initial  velocity vector of the stone with respect to earth is 48 m/s

Explanation:

According to the problem the boat is moving downstream , then the velocity of the boat with respect to the river,U(motor) =2m/s  

The velocity of the river is =1m/s

Therefore the actual velocity of motorboat=3m/s

 velocity of boat ordinary =1m/s

velocity of motorboat boat with respect to ordinary boat  =2m/s

The distance between both the boats ,d = 20 m

let the time they will collide is t

we know the equation of motion:

d=vt+1/2at^2

20=2t+0

t=10

at the same time the stone will collide the ordinary boat

d=vt+1/2 at^2

20=u*10+1/2*10*100

v=-48m/s