Question

A forensic scientist (CSI) is trying to find a weapon thrown off a bridge into the lake. Assume it is thrown horizontally and it sinks straight down once it hits the water. The bridge height is 15 meters and a normal throwing speed is 23 m/s. How far from the bridge should you search? Give the answer to the nearest whole number in meters.

Answer 1

Assuming it is thrown horizontally we have velocity in x-direction as

v_x = 23 m/s

For the vertical motion, we have

initial velocity u_y = 0

acceleration = g =9.8 m/s²

height h =15 m

time t is taken to reach the water surface

using the second equation of motion

h = u_y t + (1/2)gt²

15 = 0 + (0.5)(9.8)t²

15 = 4.9 t²

t² = 3.06

t = 1.75 s

During this time the distance covered in horizontal direction is

x = v_xt

x = 23 (1.75)

x = 40.3 m

He should search at a distance of 40.3 m far from bridge