Easiest Physics Problem Ever Why Can't I Solve

[xgeek]

Homework Statement

A diver performs a handstand dive from the 12m tower. Compute the following.
A. Time to hit the water
B. The divers velocity at 6m
C. The divers velocity at impact
D. What was the divers mean acceleration acting on the diver

Homework Equations

d=Vit + 1/2 a t^2
vf^2 = vi^2 + 2 a d
vf = vi + a t
a average = Change in velocity/Change in time

The Attempt at a Solution

A. i tried to solve for time, using equation 1 and got 1.56 seconds
B. then i tried to solve for velocity at 6m, used the same equation but used half the time and got like -3.87m/s but could I use the equation 3 and plug in half the time and the Vi as 0 and got -7.65 m/s
C. I just doubled both of those values?? to get the velocity at impact
D. I would take the final - initial divided by the time

 

[Harrisonized]

That's because you forgot a key equation:

mgh = 1/2 mv²

And life is simplified.

 

[xgeek]

i wasnt given a mass...

 

[Harrisonized]

You don't need the mass. Mass cancels from both sides of the equation. You could have derived it from your second equation though.

v_f² = v_i² + 2ad

You know that v_i=0. Therefore,

v_f² = 2ad

1/2 v_f² = ad

d is just h, the height. a is just g, the acceleration due to gravity.

1/2 v_f² = gh

1/2 mv_f² = mgh

(This last equation is just a statement of the conservation of energy.)

 

[xgeek]

youre a genius :)

 

[xgeek]

but what is time? did I do that correctly?

 

[Harrisonized]

Why do you need the time? The acceleration was constant throughout the entire process.

 

[xgeek]

the time it took for the diver to hit the water. am i overlooking something. i feel like this was soooo easy, i feel dumb

 

[Harrisonized]

Oh sorry. That was my mistake. I didn't see that your question called for that. Use the last equation.

v_f = v_i + at

You know that v_i = 0 and a = g.

 

[xgeek]

thanks :)