# Exam-style question - mechanics

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#1

I need help on part 2.4
I am not sure what to write and not entirely sure about the explanation behind it.
Last edited by Thanquinho; 3 months ago
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3 months ago
#2
Did you derive any equations for the force on the parachute that involved the density of the gas the parachute was moving through in the omitted sections?
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#3
(Original post by Joinedup)
Did you derive any equations for the force on the parachute that involved the density of the gas the parachute was moving through in the omitted sections?
Nope, section 2.3 asked to find the acceleration due to gravity when 2.2*10^5 J of kinetic energy is lost through a vertical distance of 49m. It also says during this time, 3.3*10^5 J of energy is transferred from the system to the atmosphere, and the total mass of the system is 610 kg.
So I did mgh = 2.2*10^5
Rearranged the equation to get g as 7.4m/s^2. That's for 2.3

2.4 just asks me to explain what would happen if there is an increase in dust content in the atmosphere.
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3 months ago
#4
(Original post by Thanquinho)
Nope, section 2.3 asked to find the acceleration due to gravity when 2.2*10^5 J of kinetic energy is lost through a vertical distance of 49m. It also says during this time, 3.3*10^5 J of energy is transferred from the system to the atmosphere, and the total mass of the system is 610 kg.
So I did mgh = 2.2*10^5
Rearranged the equation to get g as 7.4m/s^2. That's for 2.3

2.4 just asks me to explain what would happen if there is an increase in dust content in the atmosphere.
You'll have to try make 3 points that follow from the suspended dust increasing the density of the atmosphere...

assuming the same size parachute and initial speed, the mass of atmosphere displaced per unit time is [increased / decreased/unchanged]*
causing the tension in the parachute cords to be [greater than/lesser than/the same as]* in the original atmosphere
with the result that the deceleration is [larger/smaller/no different]*

*delete as applicable
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#5
(Original post by Joinedup)
You'll have to try make 3 points that follow from the suspended dust increasing the density of the atmosphere...

assuming the same size parachute and initial speed, the mass of atmosphere displaced per unit time is [increased / decreased/unchanged]*
causing the tension in the parachute cords to be [greater than/lesser than/the same as]* in the original atmosphere
with the result that the deceleration is [larger/smaller/no different]*

*delete as applicable
I am still not sure if the dust increasing the density of the atmoshpere will result in a bigger or smaller deceleration of the system and why that happens.

Will the system have a greater deceleration because dust is more dense and has more mass and due to Newtons 2nd law F = ma an increase in mass and constant force will result in smaller acceleration towards the ground therefore the system has a greater deceleration? Or how would I explain that displacing the gas+dust in the atmosphere will have a greater force acting in the opposite direction of the direction of travel than just displacing the gas using Newtons laws of motion?
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3 months ago
#6
The gas of the atmosphere has to move to let the parachute move through it... If the atmosphere has more mass it means more work done.
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