Determine speed (HELP PLS) (anyone there)

Question

A driver accelerating too quickly on a horizontal bridge, skids, crashes through the railing, and lands in the river 30.0 m below the level of the bridge roadway. The police find that the car is not vertically below the break in the railing, but is 60 m beyond it horizontally. Determine the speed of the car before the crash in km/hr.

Answer 1

So we want to find the horizontal speed of the car before the crash, and assuming no drag force or energy being lost as it breaks through the railing, we can find it through the equation d = vt.

We already have d, the distance the car travelled, as it is given in the problem.

So to find v, we need to find t.

Luckily, we know that the car fell 30.0 m.

The acceleration due to gravity is 9.81 m/s²

We assume the initial vertical velocity (v₀) is zero, as the car was driving on a road (and we are not given an incline)

So we can use another kinematics equation,

d = v₀t + 1/2 gt².

By plugging in the values, we have

30.0 m = 1/2 (9.81 m/s²)t²

t² = 30.0 m * 2 / 9.81 m/s² = 2.12 s²

Take the square root to get

t = 2.47 s

(-2.47 would also work for the equation, but you cannot fall for a negative amount of time)

Going back to our original equation, we have

d = vt

v = d/t = 60.0 m / 2.47 s = 24.3 m/s

From here we just convert units

24.3 m/s * 1 km / 1000 m * 3600 s / 1 hr = 87.3 km/hr