Exercise 6.8
During a high jump event, a landing mat or sand bed is placed for the athlete to fall upon (Fig. ). Explain the reason behind it.
Not cross-checked
NCERT prints no numerical answer for this exercise, so this working has not been cross-checked against the book.
The mat or sand bed increases the time taken to bring the athlete to rest, which reduces the force acting on them.
On landing, the athlete's downward velocity must fall to zero.
A soft mat or sand compresses under the athlete, so this change of velocity is spread over a longer time interval.
A longer time for the same change in velocity means a smaller magnitude of acceleration.
By Newton's second law \(\displaystyle F = ma \), a smaller acceleration means a smaller force on the athlete's body, so the risk of injury drops.
On hard ground the stop would be almost instant, the acceleration huge and the force large enough to cause injury — the same reasoning as for airbags in vehicles (Fig. $\displaystyle 6.19$).