Question

The velocity of a diver just before hitting the water is -8.6 m/s, where the minus sign indicates that her motion is directly downward. What is her displacement during the last 0.86 s of the dive?

im so stuck. i tried this problem several times, and my answers werent correct. please help me.

Answer 1

I had a problem similar to this but I was using -11.4 m/s and 1.35 s. You can use my calculations below and just plug in your numbers.


Velocity of diver just before hitting the water,Vf = - 11.4 m/s

Time, t = 1.35 s

Velocity of diver before 1.35 s = Vi

Vf = Vi - g t

- 11.4 = Vi - 9.8 * 1.35

- 11.4 = Vi - 13.23

Vi = 13.23 - 11.4

= 1.83 m/s

Displacement during 't' s , S = [ ( Vi + Vf ) /2 ] t

= [ ( 1.83 - 11.4 ) / 2 ] * 1.35

= - 6.46 m

Answer 2

Vf=Vo+gt where Vf is velocity just before hitting water, and Vo is at the start of the .86
-8.6m/s=Vo-9.8(-.86)
Vo= -8.6+8.43=-.172

So the average velocity is 8.49, displacement then is downward 8.49*.86 meters