00:01
In this problem, we have been given that there is a stone which is thrown vertically upward from the top of the building.
00:09
So let's say this is the building here.
00:11
And we have been given that the height of this building is 70 meters.
00:16
So from a height of 70 meters, a ball is thrown or let's say a stone is thrown basically with a speed of 12 meter per second.
00:25
So we need to determine that how much time it will take to strike the ground or to hit the ground.
00:33
So here we consider the foot direction as the positive direction and the downward direction as the negative direction.
00:40
So initial speed are the initial velocity taking direction into consideration that will be plus 12 meter per second.
00:47
The acceleration will be minus 9 .8 meter per second square because this is the acceleration due to gravity.
00:53
And this rock thrown from here or the stone thrown from here that will go to the maximum height and return here.
01:03
So basically in the vertical direction, this rock comes down by a position of 70 meters.
01:09
So we can definitely conclude the displacement to be minus 70 meter with respect to the point of projection.
01:16
So now we need to determine the time it takes to reach the ground.
01:21
And of course the speed with which it reaches the ground so we need to determine t in the first instance and v in the second instance so here we can first figure out we using 2 a s is equal to v square minus u square so putting the values here we get two times a that's minus 19 .6 into minus 70 that's equal to v square minus u squared that's 12 square so which is so from here we can get v square as 144 plus 19 .6 times 70...