# If a parachutist free falls, assuming he reaches terminal velocity, what is the force with which he hits the ground if he fails to open parachute?

## Is it his weight only or other forces as well. Give explanation.

Aug 5, 2018

It is dependent on the parachutist's mass, velocity, and the time taken for the mass to decelerate to zero velocity

#### Explanation:

$F = m a$

$F = m \frac{\Delta v}{\Delta t}$

$F \Delta t = m \Delta v$

This is not easy to calculate unless the deceleration characteristics are known.

If the parachutist is considered to be a rigid object and the deceleration is constant it is a fairly easy thing to work out.

This requires the mass, the change in velocity and the time it takes to come to rest.

Obviously falling into soft mud or onto a slope will increase the deceleration time, which will proportionately decrease the force required, compared to falling onto concrete or rock.

If some parts of the parachutist stop before others then it becomes rather more complicated to calculate.

(The equations still hold true, but $F$ is not likely to be constant)

The parachutist will also have the force opposing the acceleration due to gravity, which remains even after coming to rest.