Question

A ball thrown vertically upwards with a speed of 29.4 ms-1 from the top of a tower returns to the earth in 8 seconds. Find the height of the tower. (g = 9.8 ms-2)

Answer 1

$\boxed {\bf \: Hello \: there \:}$

Given that -

intial speed , u = 29.4 m/s

time , t = 8 second

height , s = ?

acceleration , g = - -9.8 m/s²

$\bf \: By \: 2nd \: equation \: of \: motion \\ \\ \boxed { \bf \: s = ut + \frac{1}{2} g {t}^{2} } \\ \\ = 29.4 \times 8 - \frac{1}{2} \times 9.8 \times 8 \times 8 \\ = 235.2 - 32 \times 9.8 \\ \\ = \boxed {- 78.4 \: m}$

negative sign indicate that it was coming down

Hope that helps you ☺

Answer 2

Answer:

-78.4 m

Explanation:

intial speed , u = 29.4 m/s

time , t = 8 second

height , s = ?

acceleration , g = 9.8 ms‐²

By2ndequationofmotions=ut+21gt2

=29.4×8−21×9.8×8×8

=235.2−32×9.8

=−78.4m

negative sign indicate that it was coming down