77. two forces act on a parachutist falling in air: the force of gravity and air resistance. if the fall is steady, with no gain or loss of speed, then the parachutist is in dynamic equilibrium. how do the magnitudes of the gravitational force and air resistance compare?

Explanation:

When a parachutist jump from an aeroplane, there are two forces acting on the parachutist.

One is the force called gravitational force which is acting downwards.

Other is the force of air resistance which is acting upwards.

When the parachute is not opened, the gravitational force is more than the air resistance force due to which the parachutist experiences a force with which he is coming down and thus , there is an acceleration in the body and the velocity of the body goes on increasing.

When the parachute is opened, the gravitational force is balanced by the air resistance force due to which there is no net force acting on the body of parachutist and thus, he comes down with uniform velocity as acceleration in the body is zero.

In this condition, the magnitude of gravitational force is equal to the air resistance force.

magnitude and direction

total distance travelled = 60 miles

total time taken =1.5 hours

average speed = total distance / total time

60 / 1.5

= 40

therefore, average speed = 40 m/h

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