Question

A boy drops a weight from the top of a bridge while a friend below measures the time it takes for the object to strike the water below. What is the height of the bridge, in units of meters, if the time is 5.5 sec?

Answer 1

Explanation:

v= 0 m/s

a = g = -10 m/s².............( negative because the object is falling )

t = 5.5 s

using first equation of motion,

v = u + at

v - at = u

0 - (-10)(5.5) = u

0 - (-55) = u

0 + 55 = u

55 m/s = u

using third equation of motion,

v² - u² = 2as

0² - 55² = 2(-10)s

0 - 3025 = -20s

-3025 = -20s

$\frac{ - 3025}{20} = - s$

-151.25 = -s

151.25 = s

Height of the bridge is 151.25 metres.