Question

A rock is dropped from a bridge and it hits the river 4.5 seconds later. How high is the bridge?

Answer 1

99 meters

Step-by-step explanation:

Apply the distance formula:

`\displaystyle{s = ut + (1)/(2) g{t}^(2) }`

where u is initial velocity which is 0 m/s since there is no initial velocity by dropping an object.

t is time which we know is 4.5 seconds. Finally, g is a constant of acceleration due to gravity which on Earth equals to 9.8 m/s². Therefore:

`\displaystyle{s = 0 \cdot 4.5 + (1)/(2)(9.8) {(4.5)}^(2) } \\ \\ \displaystyle{s = (1)/(2)(9.8) {(4.5)}^(2) } \\ \\ \displaystyle{s \approx 99 \: \text{m}}`

Therefore, the bridge is around 99 meters height.