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# EX 13: - PowerPoint PPT Presentation

EX 13:. In order to help an isolated village, a stationary helicopter releases boxes of food supplies from a height h A = 50 m. Each box is provided with a parachute.

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EX 13:

In order to help an isolated village, a stationary helicopter releases boxes of food supplies from a height hA = 50 m. Each box is provided with a parachute.

The set (S) [box, parachute] has a mass M = 50 kg.

(S), released at A without initial velocity (VA = 0), moves down along the vertical trajectory ABC and reaches B, of height hB = 45 m, with a speed VB = 10 m/s .

1) All the forces of friction are neglected while falling from A to B .The mechanical energy of (S) is conserved along the path from A to B. Why?

Mechanical energy is conserved because no friction along AB.

2) Specify the transformation of energy that takes place while falling from A to B.

As it starts to fall the potential energy begins to be transformedinto kinetic energy.

P.E reference

In order to help an isolated village, a stationary helicopter releases boxes of food supplies from a height hA = 50 m. Each box is provided with a parachute.

The set (S) [box, parachute] has a mass M = 50 kg.

(S), released at A without initial velocity (VA = 0), moves down along the vertical trajectory ABC and reaches B, of height hB = 45 m, with a speed VB = 10 m/s .

• 3)Upon reaching B, the parachute opens and the set (S) continues its fall at a constant speed of 10m/s until it reaches C (VC =10 m/s).
• Find the decrease in the mechanical energy of (S) when it passes from B to C.

In order to help an isolated village, a stationary helicopter releases boxes of food supplies from a height hA = 50 m. Each box is provided with a parachute.

The set (S) [box, parachute] has a mass M = 50 kg.

(S), released at A without initial velocity (VA = 0), moves down along the vertical trajectory ABC and reaches B, of height hB = 45 m, with a speed VB = 10 m/s .

• 4) How does this loss of energy appear?

It appears in the form of heat energy (thermal heat)

4) One of the parachutes did not open while falling from A to C. Determine, in this case, the speed with which this box reaches C.

Mechanical energy is conserved because no friction along BC then :

2

5- What can you conclude about the role of the parachute in the fall of the box?

• The parachute reduces the speed of the box upon impact with the ground.