# A Diver jumps into water

1. Jul 23, 2009

### xicedcandyx

how do you solve a problem like this? a diver jumps into the water. what is the force exerted by the water? we are only given the mass of the diver

i know it has to do with energy (gravitational and potential?), but i don't know how to do it.

2. Jul 23, 2009

### Staff: Mentor

What are your thoughts on how do do it? Does the diver's velocity change when they hit the water? What do you know about velocity changes and what causes them?

3. Jul 23, 2009

### xicedcandyx

1. a 10 kg diver dives into a pool. what is the average force the water exerts on the man?

2. W= Fnet * $$\Delta$$r
KE= 1/2 mv2
W= F $$\Delta$$r cos$$\theta$$

3. W= F$$\Delta$$r cos$$\theta$$
W= -Fwaterd

do i have enough info?

4. Jul 23, 2009

### xicedcandyx

isn't velocity 0 when the diver hits the water? velocity changes are caused by force according to Newton's 1st law. sooo the force of the water changes the velocity? i still don't get how to find the force the water exerts if i only have the mass :(

5. Jul 23, 2009

### Staff: Mentor

The velocity of what? The diver is moving down when he hits the water, and is decelerated smoothly as he enters the water and goes down a ways to a stop.

You are right that the water exerts a force during that time, which causes the deceleration. The deceleration may have a constant rate or not, depending on your assumptions.

Pick a total decelration time, and assume a constant deceleration, and calculate the water force required. Then pick a total time that is half of the first one you chose. How much does the average force go up?

6. Jul 23, 2009

### Referos

No, I don't think there's enough info to solve this. Unless I am mistaken, we need to know from which height the diver jumped (or at least his speed when he entered the water), and how much he moved once in the water.

And the diver's mass is 10kg? Did your mean 100kg?

7. Jul 23, 2009

### turin

Or, it's a "trick" question ... (i.e. too much info). How much of a difference does it make if the diver dives or just climbs in? I suppose one other piece of info, which must be assumed, is that a person is most likely very slightly less dense than water.

8. Jul 23, 2009

### Staff: Mentor

(The two threads on the same question merged into one...)

9. Jul 23, 2009

### Referos

Wait, are you supposed to reach a numerical answer (e.g., 5N)? Or can it be in terms of other variables or parameters?

10. Jul 23, 2009

### DaveC426913

Zero; he's still dry.

However the force his wife exerts on him for having just dropped their 1 year old baby in the pool is substantial.