Question

A ball is thrown directly downward with an initial speed of 8.45 m/s, from a height of 29.9 m. After what time interval does it strike the ground? s

Answer 1

Given:

The initial speed of the ball is: u = 8.45 m/s.

The ball is thrown from the height: h = 29.9 m

To find:

The time ball takes to strike the ground.

Step-by-step explanation:

The time taken by the ball to strike the ground can be determined by using the following equation.

`x=ut+(1)/(2)at^2`

Here, x = -29.9 m, u = -8.45 m/s and a = -9.8 m/s^2. The negative sign indicates that the ball is falling in the downward direction.

Substituting the values in the above equation, we get:

`\begin{gathered} -29.9=-8.45t-(1)/(2)*9.8t^2 \\ \\ 4.9t^2+8.45t-29.9=0 \end{gathered}`

Solving the above quadratic equation, we get:

t = 1.754 s and t = -3.478 s

But the time is never negative, thus t = 1.754 s.

Final answer:

The ball takes 1.754 seconds to strike the ground.