Question

a student drops a rock from the top of a bridge. how fast is the rock moving after falling for 3 seconds? assume that the rock does not hit the ground in 3 seconds and air resistance is negligible. a 10 m/s b 30 m/s c 60 m/s d 90 m/s

Explanation:

Step1: Recall the free - fall velocity formula

When an object is in free - fall (neglecting air resistance), the velocity of the object at time \(t\) is given by the formula \(v = gt\), where \(g\) is the acceleration due to gravity. The approximate value of \(g\) near the Earth's surface is \(g= 10\space m/s^{2}\) (or sometimes \(9.8\space m/s^{2}\), but for simplicity, we use \(10\space m/s^{2}\) here).

Step2: Substitute the values into the formula

We are given that the time \(t = 3\space s\) and \(g = 10\space m/s^{2}\). Substituting these values into the formula \(v=gt\), we get \(v=10\times3\).

Step3: Calculate the result

\(10\times3 = 30\space m/s\).

Answer:

B. 30 m/s