A boy throws a ball at an angle 450 with the horizontal at t = 0 at origin. Path of the ball follows the trajectory y = x – 5x2. The boy start running with a constant velocity 1 m/s along x-axis at t = 0. Take g = 10 m/s2. Choose correct option/s.
(a) Boy and ball are in same vertical line at each instant of time.
(b) At t = 0.1 s, velocity of ball w.r.t. boy = zero.
(c) At t = 0.2 s, ball hits boy.
(d) Ball never hits boy.
71Easy one I think...
It's (a). Am I right?
Comparing Directly with Trajectory EQuation we have,
\frac{g}{2(u cos \theta) ^{2}} = 5
=> Solving we have u cos \theta = 1
=> I.e., Velocity in Horizontal direction is 1 m/sec == Velocity of boy i Horizontal direction.
Thus Ans is (a).
Am I right?
30Oh yes.. A very stupid calc. mistake..
This is how I did it.
y= x -5x2
At max. horizontal displacement y=0,
5x2=x => x=1/5 (over here, I calculated x=5 :P)
1/5 = u2/g
u = √2
therefore, ucosθ = 1 and hence ans. should be (a)
1Its multiple correct qs of Test Series from vidyadrishti.com. I also got the same ans. First part is ok. But I think more options are correct.
1i think ans will be a,b,c
(a) has been explained by vivek
(b) because t=0.2 is time period of the ball
so at t=0.1 ball would be moving horizontally with velocity ucosθ i = i (unit vector i)
and at that instant velocity of boy also = i
so relative velocity = 0
(c) because at t= 0.2 the ball would have covered same horizontal distance as boy
so it would hit the boy
71Yes b and c are is also correct. But d is wrong I think.
71Did you get your solutions or cleared your doubt? @Shams
