Kinematics Question: Metal Box and Parachute Freefall Calculation

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In summary, a metal box, attached to a small parachute, is dropped from a helicopter. The resultant force of the box and parachute at a particular instant during its fall is 20N. The combined mass of the box and parachute is 5.0 kg.
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n707jt
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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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  • #2
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?
 
  • #3
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.
 
  • #4
n707jt said:
Is it simply (24+0)/2 ? Correct me if I am wrong please.
Yes, that is correct.
 
  • #5
Doc Al said:
Yes, that is correct.

Thank you very much.
 

What is simple kinematics?

Simple kinematics refers to the study of motion without considering the causes or forces behind it. It focuses on the position, velocity, and acceleration of an object without taking into account the forces that may be acting on it.

What is the difference between kinematics and kinetics?

Kinematics is the study of motion without considering the forces involved, while kinetics is the study of the forces that cause motion. In other words, kinematics looks at the "what" of motion, while kinetics looks at the "why" of motion.

What are the three basic kinematic equations?

The three basic kinematic equations are:
1. v = u + at (final velocity = initial velocity + acceleration * time)
2. s = ut + 1/2at^2 (displacement = initial velocity * time + 1/2 * acceleration * time^2)
3. v^2 = u^2 + 2as (final velocity^2 = initial velocity^2 + 2 * acceleration * displacement)

What are some examples of simple kinematics problems?

Some examples of simple kinematics problems include:
1. Calculating the distance a car travels in a certain amount of time given its initial velocity and acceleration.
2. Finding the final velocity of an object dropped from a certain height given its initial velocity and the acceleration due to gravity.
3. Determining the time it takes for a ball to roll down an incline plane given its initial velocity and the angle of the incline.

How is kinematics used in everyday life?

Kinematics is used in everyday life in many ways, including:
1. Driving a car - understanding the relationship between speed, distance, and time helps us control our vehicles safely.
2. Sports - athletes and coaches use kinematics to analyze and improve performance in activities such as running, throwing, and jumping.
3. Motion sensors - these are used in many devices such as smartphones and gaming consoles to track movement and calculate position and velocity.

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