Question

A knight sits on a castle wall during a siege. To while away the time, he notes that boulders catapulted from below land on the top of his wall with a vertical velocity of 5.6 m/s. If he is 39 m above the catapult, what is the initial velocity of the boulders? The acceleration of gravity is 9.8 m/s 2 . Answer in units of m/s.

Answer 1

Answer:

v = 28.21 m/s

Explanation:

given,

vertical velocity of the boulder = 5.6 m/s

height of catapult = 39 m

initial velocity = ?

acceleration due to gravity = 9.8 m/s²

maximum height attained

v² = u² + 2 as

5.6² =  = 2 g h

$h = \dfrac{5.6^2}{2\times 9.8}$

h = 1.6 m

total height above catapulted

H = 39 + 1.6 = 40.6 m

$v = \sqrt{2gh}$

$v = \sqrt{2\times 9.8 \times 40.6}$

v = 28.21 m/s

so the intial velocity is equal to v = 28.21 m/s