How Fast Does a Girl Enter the Water When Diving from a 15m Platform?

[meawinner]

Hi this is an AS physics question that i am stuck on. I tried it but I don't get the answer it says in the answers.

A girl diving froma 15m plstform wishes to know how fast she enters the water. She is in the air for 1.75s and dives from rest(with an initial speed of zero). What can you tell her about her entry speed?

I tried to do speed=distance over time
Then I used acceleration is final velocity-initial velocity over time. But neither worked so can some1 please help me. Thanks

 

[Jimmy]

Hello meawinner,

Since Vf = Vi + a t, and the acceleration is just that of gravity, it is a simple calculation.

Vf=Vfinal, Vi=Vinitial, a=acceleration, t=time.

Alternately, you could us the formula Vf = Vi + sqrt(2 a d)

 

[M98Ranger]

Hi there,

It sounds like you are on the right track with using the equations for speed and acceleration. However, in this scenario, the girl's initial velocity is zero, so we can simplify the equation to just:

v = a * t

where v is the final velocity (or entry speed in this case), a is the acceleration due to gravity (which is -9.8 m/s^2 for objects falling near the Earth's surface), and t is the time in seconds.

To solve for v, we can plug in the values given in the problem:

v = (-9.8 m/s^2) * (1.75 s)

This gives us a final velocity of -17.15 m/s. Since velocity is a vector quantity, the negative sign indicates that the girl is moving downwards (or in the direction of gravity) when she enters the water.

I hope this helps you understand the problem better. Keep up the good work and don't be afraid to ask for help when you need it!