Force exerted by water on diver (2nd law of Motion)

In summary, the high diver in the question has a mass of 68.4 kg and jumps off a 9.5 m board into water with an acceleration of gravity of 9.8 m/s^2. After entering the water, his downward motion is stopped after 5.92 seconds. To find the average upward force exerted by the water on him, the acceleration of the water must be first calculated using the equation v = v0 + at. Upon solving, an acceleration of -15.726 m/s^2 is found. This is then used in the equation F = ma, resulting in an average force of -1075.682 N. However, upon checking with Quest, the answer is incorrect. It
  • #1
bydesign
2
0
I've been in my physics class for almost two months now, and I'm starting to run into trouble. I think I'll be around here for a while, assuming you guys can help me out ;)

The Question : A high diver of mass 68.4 kg jumps off a board 9.5 m above the water.
The acceleration of gravity is 9.8 m/s2 .
If his downward motion is stopped 5.92 s after he enters the water, what average upward
force did the water exert on him?
Answer in units of N.

Homework Equations

:
v = v0 + at (To determine acceleration
EF (Average Force) = ma

The Attempt at a Solution

:
Well, I first have to find the acceleration of the water on the swimmer :
v = v0 + at
0 = (9.5m*9.8m/s^2) + a (5.92)
-93.1 = a (5.92s)
-15.726 m/s^2 = a

Now I plug that into F = ma
F = ma = (68.4 kg) (-15.726 m/s^2) = -1075.682 N

This looks about right, but when I put it into Quest, it comes out wrong. I've checked my math over twice. What am I doing wrong?

Thanks for the help :)
 
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  • #2
you put t=5.92, but that is for when he now enters the water.

so in v=u+at

we want v=0, but the diver doesn't enter the water with 0 velocity. So you need to find this velocity 'u'. (try using conservation of energy to find this velocity)
 
  • #3
Thank you very much - that helped me a bunch ;)
 

Related to Force exerted by water on diver (2nd law of Motion)

What is the second law of motion?

The second law of motion, also known as Newton's second law, states that the force exerted on an object is equal to its mass multiplied by its acceleration. In other words, the greater the mass of an object and the greater its acceleration, the greater the force exerted on it.

How does this law apply to a diver in water?

When a diver jumps into water, they experience a force exerted by the water that pushes them in the opposite direction. This is due to the fact that the diver's mass stays the same, but their acceleration increases due to the resistance of the water. This force can be calculated using the equation F=ma, where F is the force, m is the mass of the diver, and a is the acceleration.

What factors affect the force exerted by water on a diver?

The force exerted by water on a diver can be affected by various factors such as the speed of the diver, the density of the water, and the shape of the diver's body. The force will also vary depending on whether the diver is moving vertically or horizontally in the water.

How does the force exerted by water on a diver impact their motion?

The force exerted by water on a diver can impact their motion by either slowing them down or propelling them forward. This force is also responsible for the diver's buoyancy in the water, which can affect their ability to control their movement and stay afloat.

What are some real-life applications of the second law of motion in relation to water and diving?

The second law of motion has various real-life applications in relation to water and diving. For example, understanding this law can help divers calculate the amount of force they need to exert in order to move through the water efficiently. It can also be used in designing equipment such as scuba diving gear and submarines, to ensure they can withstand the forces of water and move effectively.

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