When jumping straight down, you can be seriously Injured If you land stiff-legge

Question

When jumping straight down, you can be seriously Injured If you land stiff-legged. One way to avoid injury is to bend your knees upon landing to reduce the force of the Impact. A man Just before contact with the ground has a speed of 6.9 m/s. In a stiff-legged landing he comes to a halt in 2.2 ms. Find the average net force that acts on him during this time. When he bends his knees, he comes to a halt in 0 09 s. Find the average force row. During the landing, the force of the ground on the man pants upward, while the force due to gravity points downward. The average net force acting on the man includes these forces. Taking Into account the directions of these fortes, find live forte of the ground on the man in parts and stiff legged landing bent legged landing

Explanation / Answer

m= mass = 75 kg

let upward direction of force = +ve, downward direction = -Ve

So initial speed = u = - 6.9 m/s

V = final velocity = 0

a) t = time = 2.2 ms

F_avg = average force = m*a ( a= acceleration = (V-u)/t)

F_avg = m*( V-u ) / t

= 75*( 0 - (-6.9) / 2.2*10-3 = 2.35*105 N

b) now t= 0.09 s

F_avg = m*( V-u ) / t

= 75*( 0 - (-6.9) / 0.09 = 5.75*103 N

c) F_avg (net average force) = F_ground - W

F_ground = force of ground in upward direction

W = weight = mg ( in downward direction) = 75*9.8 = 735 N

F_ground = F_avg + W

stiff legged , F_ground = 2.35*105 + 735 = 2.35735*105 N

bent legged , F_ground =  5.75*103 + 735 = 6.485*103 N

Related Questions

Navigate

• Browse (All)
• Browse W
• Subjects

---

---

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.