Force and acceleration leading to weight of a parachutist

In summary, the question is asking for the parachute with the largest upward force, not the one with the largest net force. The answer is A, because the velocity has the largest impact on the force.
  • #1
Mukilab
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Homework Statement



http://www.physics.ox.ac.uk/olympiad/Downloads/PastPapers/BPhO_PC_2008_QP.pdf

Question 8

Homework Equations



f=ma

The Attempt at a Solution



Sure since f=ma
A) would have force of 0, since there is no acceleration
B) force would be 800N
C) force of 0N
D) force of 0N
E) Force of 1000N (10 m/s^2 due to gravity)

so surely E would be the answer? I just don't understand why A is the answer (it is in the mark scheme that A is the answer).

Plus, how on Earth do you add in the 'extra-large parachute' thing?

Any help would be great thanks
 
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  • #2
well, remember that the question is just asking for the one with the largest upward force, not the one with the largest net force.

And remember which direction the force of gravity points.
 
  • #3
SHISHKABOB said:
well, remember that the question is just asking for the one with the largest upward force, not the one with the largest net force.

And remember which direction the force of gravity points.

Well drag = kAv^2

But for some of the parachutes we don't know the area of 'extra-large' so what can we do?

(if we ignore extra-large etc, A is right, thank you very much for your help)
 
  • #4
well if you look at kAv2, we can see that the velocity has the largest impact on the force

let's say the normal parachute has area A. Let's also ignore k for the moment since I assume it's the same for each parachute.

So for each of them (other than E) we have 36A, A, 16A and then 4 times the area of the large parachute.

The extra large parachute would have to be nine times as large as the normal parachute to get the same amount of drag force. Since nine times the area is a bit excessive, I'd go with answer A.
 
  • #5
SHISHKABOB said:
well if you look at kAv2, we can see that the velocity has the largest impact on the force

let's say the normal parachute has area A. Let's also ignore k for the moment since I assume it's the same for each parachute.

So for each of them (other than E) we have 36A, A, 16A and then 4 times the area of the large parachute.

The extra large parachute would have to be nine times as large as the normal parachute to get the same amount of drag force. Since nine times the area is a bit excessive, I'd go with answer A.

Thank you very much, problem resolved :)
 

Related to Force and acceleration leading to weight of a parachutist

1. What is force and how does it affect a parachutist's weight?

Force is a physical quantity that describes the interaction between objects. When a parachutist jumps out of a plane, the force of gravity begins to act on them, causing them to accelerate towards the ground. As the parachutist falls, the force of air resistance also begins to act on them, pushing against the force of gravity and slowing their acceleration. This results in a decrease in the parachutist's weight as they fall.

2. How does acceleration play a role in a parachutist's weight?

Acceleration is the rate of change of an object's velocity. In the case of a parachutist, acceleration is directly related to the force acting on them. As the force of gravity increases, the parachutist's acceleration towards the ground increases, resulting in a decrease in their weight. As the force of air resistance increases, the parachutist's acceleration decreases, resulting in an increase in their weight.

3. How does the weight of a parachutist change during freefall?

During freefall, the weight of a parachutist decreases as they accelerate towards the ground due to the force of gravity. As they reach terminal velocity, the forces acting on them are balanced, resulting in a constant weight until they reach the ground.

4. How does weight affect the speed of a parachutist's descent?

The weight of a parachutist affects the speed of their descent due to the force of gravity. A heavier parachutist will experience a greater force of gravity and therefore a higher acceleration, resulting in a faster descent. Conversely, a lighter parachutist will experience a lower force of gravity and a slower descent.

5. How does air resistance impact a parachutist's weight during descent?

The force of air resistance acts against the force of gravity, slowing the parachutist's acceleration towards the ground. This results in a decrease in the parachutist's weight during descent. As the parachutist's speed decreases, the force of air resistance also decreases, resulting in a decrease in their weight until they reach terminal velocity.

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