This is a suggested answer to the GCE O Level Pure Physics examination, year 2017, Paper 1, multiple choice question 5.

The question stated that a parachutist is falling through air when he opens his parachute. The following data is given:

  • Mass of parachutist is 80kg
  • After the parachute opens, the total air resistance is 2400N
  • Gravitational field strength is 10N/kg

The student is required to calculate the initial deceleration after the parachute opens.

Suggested Solution:

The answer is B. That is, the deceleration is 20m/s2

Explanation:

When the parachutist is falling through air. The resultant force is the result of the two forces:

Weight of the parachutist, given as:

      W=80 kg x 10N/kg=800N

And opposing air resistance, given as 2400N.

The resultant force is therefore 2400N-800N =1600N

However, the formula of resultant force is:

Resultant Force, F = Mass x acceleration

       hence, the deceleration, a   = 2400N/80kg

    = 20m/s2