I have done this problem over and over but cannot figure outhow to get it! Help?

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I have done this problem over and over but cannot figure outhow to get it! Help?
When jumping straight down, you can be seriously injured ifyou land stiff-legged. One way to avoid injury is to bend yourknees upon landing to reduce the force of the impact. A 75-kg manjust before contact with the ground has a speed of 5.7 m/s. (a) In a stiff-legged landing he comes to ahalt in 1.6 ms. Find the average net forcethat acts on him during this time.
N

(b) When he bends his knees, he comes to a halt in 0.09 s. Find the average force now.
N

(c) During the landing, the force of the ground on the man pointsupward, while the force due to gravity points downward. The averagenet force acting on the man includes both of these forces. Takinginto account the directions of these forces, find the force of theground on the man in parts (a) and (b). stiff legged landing N bent legged landing N I have done this problem over and over but cannot figure outhow to get it! Help?
When jumping straight down, you can be seriously injured ifyou land stiff-legged. One way to avoid injury is to bend yourknees upon landing to reduce the force of the impact. A 75-kg manjust before contact with the ground has a speed of 5.7 m/s. (a) In a stiff-legged landing he comes to ahalt in 1.6 ms. Find the average net forcethat acts on him during this time.
N

(b) When he bends his knees, he comes to a halt in 0.09 s. Find the average force now.
N

(c) During the landing, the force of the ground on the man pointsupward, while the force due to gravity points downward. The averagenet force acting on the man includes both of these forces. Takinginto account the directions of these forces, find the force of theground on the man in parts (a) and (b). stiff legged landing N bent legged landing N stiff legged landing N bent legged landing N

Explanation / Answer

F t = (m v)      impulse = change in momentum F = m v / t F = 75 * (5.7 / 1.6 * 10 E-3) = 2.67 * 10E5N      force for stiff leggedlanding F = 75 * (5.7 / .09) = 4.75 * 10E3 N    for bent knee landing The third part is a little confusing The above holds if gravity was not present (for instance inouter space and landing on an immovable surface) The force of gravity after the man lands is 75 * 9.8 = 735N One could assume that average force during landing is 1/2 ofthis since when the man initially lands the ground will be supporting none of his weight You could try adding 368 N to the above results, but I'm notquite sure what the question means here Apparently, not from a textbook because the question appears alittle ambiguous

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