Kinematics Question: Metal Box and Parachute Freefall Calculation

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Homework Help Overview

The problem involves a metal box attached to a parachute that is dropped from a helicopter. The discussion focuses on calculating the resultant downward force, the velocity at which the box strikes the ground, the average velocity during the fall, and the distance fallen, given specific forces and mass.

Discussion Character

  • Exploratory, Conceptual clarification, Mathematical reasoning

Approaches and Questions Raised

  • Participants discuss the calculation of resultant forces and question the application of Newton's laws, particularly whether the problem should be approached as an 'F=ma' scenario or through vector addition. There are attempts to calculate the final velocity and average velocity, with some participants seeking confirmation on their reasoning.

Discussion Status

The discussion is active, with participants providing calculations and seeking clarification on specific aspects of the problem. There is acknowledgment of correct answers, but also a caution regarding the reasoning behind the calculations. Guidance has been offered regarding the average velocity calculation, with participants engaging in a back-and-forth to validate their understanding.

Contextual Notes

Participants are navigating through the assumptions related to forces acting on the box and parachute, as well as the implications of the parachute being caught on a tree before the box falls freely. There is also a focus on the time of fall and the initial conditions provided in the problem statement.

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Homework Statement


A metal box, attached to a small parachute, is dropped from a helicopter.

The total force opposing the motion of the box and parachute at a particular instant during its fall is 30N. The combined mass of the box and parachute is 5.0 kg. Calculate the resultant downward force on the box and parachute (assume g = 10 m/s²).

At the end of the fall, the parachute is caught on a tall tree. The box is then cut loose and falls from rest to the ground. The time of fall is 2.4 seconds. Calculate

i) the velocity which the box strikes the ground.
ii) average velocity during the fall
iii) the distance fallen


Homework Equations





The Attempt at a Solution



I calculated the resultant force of the box and parachute to simply be:

F(resultant) -f = ma
F(resultant) - 30 ( 5 x 10)
F(resultant) = 20N

I have also calculated the velocity which the box strikes the ground.

i) a = (v-u)/t
10 = v-0/2.4
v =24m/s

For the average velocity during the fall, can someone advise me what would it be?
 
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n707jt said:
I calculated the resultant force of the box and parachute to simply be:

F(resultant) -f = ma
F(resultant) - 30 ( 5 x 10)
F(resultant) = 20N
Correct answer, but be careful with your reasoning. This is not an 'F=ma' problem, but just a problem in adding vectors to find ΣF.

I have also calculated the velocity which the box strikes the ground.

i) a = (v-u)/t
10 = v-0/2.4
v =24m/s
OK.

For the average velocity during the fall, can someone advise me what would it be?
You have the initial and final velocities, so what do you think?
 
Doc Al said:
Correct answer, but be careful with your reasoning. This is not an 'F=ma' problem, but just a problem in adding vectors to find ΣF.


OK.


You have the initial and final velocities, so what do you think?

Is it simply (24+0)/2 ? Correct me if I am wrong please.
 
n707jt said:
Is it simply (24+0)/2 ? Correct me if I am wrong please.
Yes, that is correct.
 
Doc Al said:
Yes, that is correct.

Thank you very much.
 

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