Question

When Juan Pablo reaches 50 m/s a wall suddenly pops up in his lane and he hits it, coming to a complete stop in 0.35 m. What force is required to stop him at this rate?

Answer 1

look the question says that juan pablo (jp) stops completely after 0.35 m after hitting the wall
so when he travels 0.35 m, his velocity=0
initially , he was running with a velocity of 50m/s
so we can apply the kinematical equation
v^2 - u^2=2as
where v=final velocity(here it is 0)
u= initial velocity = (here) 50m/s
s=displacement between this velocity change from u to v = (here)0.35m
and a = acceleration
so by putting the given values in the equation, we get a=-3571.42 m/s^2
and we know that Force=mass x acceleration
so you may need the mass here
if you are given the mass n the question , you candirectly multiply it with the acceleration or else i'm uploading a solution in an another way(by using impulse-momentum concept)and i think this may help
hope this helps you

Answer 2

and the acceleration was -ve as it is acting in the opposite direction of the velocity

Answer 3

now i realise that if you do it in any way, you need the mass of the man

Answer 4

@adrianf you there??