Solving Skydiving Problems: Acceleration & Air Resistance

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In summary: You can ADD 749.7 to both sides, or MULTIPLY both sides by a number, but you can't just move it.So you want to solve for "a", and you have Fnet = 749.7 = ma. That means that a = Fnet/m, right? So what you really want to do is to divide both sides of the equation by m. If you do that, you will geta = Fnet/m = (749.7/m) = __________ m/s^2 (downward) Now you just have to figure out what the mass is. The mass is given in the problem statement, right? But you have to use the right
  • #1
confusedaboutphysics
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(a) What is the acceleration of two falling sky divers (mass 102.0 kg including parachute) when the upward force of air resistance is equal to one-fourth of their weight?
________ m/s2 (downward)

(b) After popping open the parachute, the divers descend leisurely to the ground at constant speed. What now is the force of air resistance on the sky divers and their parachute? See Fig. 4-34.
_____ N (upward)

i need help on starting this problem...like what equation(s) would i use??

thanks so much!
 
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  • #2
confusedaboutphysics said:
like what equation(s) would i use??

Instead of immediately looking for an equation, try thinking about the problem.

(a) What is the acceleration of two falling sky divers (mass 102.0 kg including parachute) when the upward force of air resistance is equal to one-fourth of their weight?

If the sky divers are subjected to an upward force equal to one-fourth of their total weight, then what is the net force acting on them?

Once you determine that, then think about what law of physics relates net force (which you will have determined by this time) to acceleration (which is what the question is asking for).

(b) After popping open the parachute, the divers descend leisurely to the ground at constant speed. What now is the force of air resistance on the sky divers and their parachute? See Fig. 4-34.

If the divers' speed is constant, then what is their acceleration? What then can you say about the net force acting on them?
 
  • #3
can someone tell me if I'm doing this right for part A?

Fnet = 102(9.8) - (.25)(102)(9.8)
Fnet = 999.6 - 249.9
Fnet = 749.7 = ma

so if I'm doing this right..where do i go from here?
 
  • #4
confusedaboutphysics said:
can someone tell me if I'm doing this right for part A?

Fnet = 102(9.8) - (.25)(102)(9.8)
Fnet = 999.6 - 249.9
Fnet = 749.7 = ma

So far, so good. Just make sure that you understand that you have elected to take the downward direction as positive. Nothing wrong with that, but you'll find that most physics books choose the opposite convention.

so if I'm doing this right..where do i go from here?

What does the question ask you for?
 
  • #5
so i know I'm trying to find the acceleration..so would i plug in the answer i got for the mass?

Fnet = 749.7 = ma
Fnet = 749.7a?? but how can i solve from here if i don't know the Fnet and I'm looking for a?
 
  • #6
You do have the net force! You even stated it:

Fnet = 749.7 = ma

So you now know 749.7 = ma or a = 749.7/m

Make sure you understand the definiton of net force.

You set 749.7 = m which isn't correct - think of units.
 
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  • #7
thanks tom and cscott! i understand it much better now
 
  • #8
Not a problem. :smile:
 
  • #9
confusedaboutphysics said:
Fnet = 749.7 = ma
Fnet = 749.7a??

Have you taken algebra? You can't just move the "a" from one side of the equals sign to the other like that.
 

1. What is acceleration and how does it affect skydiving?

Acceleration is the rate at which an object's velocity changes over time. In skydiving, acceleration is affected by various factors such as gravity, air resistance, and the mass of the skydiver. As the skydiver falls, they experience a constant acceleration due to the force of gravity.

2. How does air resistance play a role in skydiving?

Air resistance, also known as drag, is the force that opposes the motion of an object through air. In skydiving, air resistance increases as the speed of the skydiver increases. This force acts in the opposite direction of motion and works to slow down the skydiver's fall.

3. How do skydivers calculate their terminal velocity?

Terminal velocity is the maximum speed a falling object can reach when the force of gravity is equal to the force of air resistance. Skydivers can calculate their terminal velocity by taking into account their weight, surface area, and air density. Generally, the average terminal velocity for a skydiver in a belly-to-earth position is around 120 mph.

4. What are some common problems that skydivers face related to acceleration and air resistance?

Some common problems that skydivers face include experiencing a higher than expected acceleration due to sudden changes in air density or wind patterns, or encountering higher than expected air resistance due to their body position or equipment malfunctions. Both of these issues can affect the skydiver's ability to control their descent and land safely.

5. How do scientists and engineers work to solve skydiving problems related to acceleration and air resistance?

Scientists and engineers use mathematical equations and simulations to model and predict the effects of acceleration and air resistance on skydivers. They also conduct experiments and gather data to better understand these forces and develop solutions, such as designing more efficient parachutes and protective gear, to help skydivers safely overcome these challenges.

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