Kinematics Question: Metal Box and Parachute Freefall Calculation

[n707jt]

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?

 

[Doc Al]

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?

 

[n707jt]

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.

 

[Doc Al]

Is it simply (24+0)/2 ? Correct me if I am wrong please.

Yes, that is correct.

 

[n707jt]

Yes, that is correct.

Thank you very much.