The answer is d) 7 seconds.
Because the ball was launched at a
Since you have no information about the distance from the tower the ball travelled in its flight, you're going to have to turn to the vertical component of its trajectory.
So, vertically, the ball starts at a height of 70 m. This means that, when it reaches ground level, the total vertical displacement will be equal to -70 m.
Think of its like this - when it hits the ground, the ball is 70 meters lower than its starting position.
This means that you can write
Plug in your values into the above equation to get (use
Solving this quadratic equation will get you
Therefore, the ball reaches the ground in