Diving Board to Diver's Stopping Point: Solve the Distance

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Homework Help Overview

The problem involves a diver stepping off a diving board and dropping into the water, where the diver experiences forces both above and below the water's surface. The objective is to determine the total distance from the diving board to the diver's stopping point underwater, given the diver's mass and the net force exerted by the water.

Discussion Character

  • Exploratory, Assumption checking, Conceptual clarification

Approaches and Questions Raised

  • Participants discuss the forces acting on the diver both before and after entering the water, including gravitational force and the net force from the water. There are attempts to set up equations for work done in both scenarios, with some participants expressing confusion about the relationship between work and distance.

Discussion Status

Participants are actively exploring different approaches to relate the work done above and below the water. There is an ongoing examination of the signs of work and the implications for kinetic energy, with some guidance provided regarding the nature of forces and work in each phase of the diver's motion.

Contextual Notes

There is a recognition of the need to define the distance from the diving board to the water surface, which is a variable in the equations being discussed. Participants are grappling with the implications of negative and positive work in relation to the diver's kinetic energy.

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Homework Statement


a 50 kg diver steps off a diving board and drops straight down into the water. The water provides an upward average net force of 1500 N. If the diver comes to rest 5.0m below the water's surface, what is the total distance between the diving board and the diver's stopping point under water?


Homework Equations





The Attempt at a Solution


the total force would be Fn-Fg which is 1500-50*9.81=1009.5N
W=1009.5*(x+5)

i am completely lost on what to do next. please give me a clue or something.
 
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princesspriya said:
the total force would be Fn-Fg which is 1500-50*9.81=1009.5N
That's the total force on the diver when he's in the water. What about before he hits the water?
 
oo it wud b fg which is 50*9.81 which is 490.5 . but that doesn't help.
 
Last edited:
Sure it helps. There are several ways to solve this kind of problem. One way would be to compare the work done on the diver before he hits the water to the work done on him after he hits the water. After all is said and done, what must the total work (by all forces) be on the diver?
 
well you don't know the distance so you cannot find the total work done.
 
Think what total work means in reference to his original state (position and velocity) and final state.
 
princesspriya said:
well you don't know the distance so you cannot find the total work done.
The distance is what you are asked to find. Try calling the distance from board to water surface D (or whatever). Now set it up and see if you can solve for D. (Then use it to get the total distance.)
 
you cannot because you would have two unsolved, the work net and the distance.
 
Try it and see. The only unknown is the distance.
 
  • #10
W=1009.5*(x+5) and W=490.5x
are those two equations correct?
 
  • #11
princesspriya said:
W=1009.5*(x+5) and W=490.5x
are those two equations correct?
No.

The diver travels a distance x before hitting the water. What net force acts? What's the net work? Is it positive or negative?

The diver travels 5 m under the water. What net force acts? What's the net work? Is it positive or negative?

What must those two work contributions add to? (Hint: What's the change in KE?)
 
  • #12
well when he is in water the work he does would be 1500N*5m because that's the distance he z traveling and the net force is 1500. so the work done would be 7500J.
The work he does under water would not be the same as above water would it?
 
  • #13
princesspriya said:
well when he is in water the work he does would be 1500N*5m because that's the distance he z traveling and the net force is 1500. so the work done would be 7500J.
1500 N is the force of the water, not the net force. You found the net force in post #1.

The work he does under water would not be the same as above water would it?
Something like that. What are the signs of the two work contributions?
 
  • #14
the work done above water would be negative while the word done below water would be positive. but how can both of them have the same magnitude? that's the part i don't understand.
 
  • #15
princesspriya said:
the work done above water would be negative while the word done below water would be positive.
Just the opposite. Above the water, the work done on the diver is positive: the force (gravity) acts in the same direction as the displacement. Below the water, the net force acts up while the displacement is still down; so the work on the diver is negative.
but how can both of them have the same magnitude? that's the part i don't understand.
Above the water, the diver's KE increases as he falls (since work is being done on him); below the water, it decreases (since negative work is being done on him). It all has to balance out, since he starts with 0 KE and ends up with 0 KE.
 

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