a stone is thrown from a bridge at an angle of 30 degress down with the horizontal with a velocity of 25 m/s.if the stone strikes the water after 2.5 seconds then calculate the height of the bridge from the water surface.'(g=9.8 m/s2)
Answers
When the stone is thrown, let's assume it starts from a point A, with a given velocity and angle according to the question. Also, let's consider the difference between the height of the water and the bridge to be h.
As the stone is thrown, it will follow a perfectly symmetric projectile motion upto the point B. (For which we have all the equations of motion.)
Now, I'll assume that the total motion to be divided into two motions, from A to B and B to C respectively.
If I can find the time the stone takes to travel from A to B, I can subtract that from the total travel time ( 2.5 seconds according to the question ) and obtain the time it takes to travel from B to C.
So, T(AB) = 2uSin30/g = 2.5 seconds.
Well, what does this mean ? It takes 2.5 seconds to go from A to B and thus 0 seconds from B to C. Meaning, h = 0 or, the water surface is level with the bridge.