Calculating Superman's Average Force (due in 4 days)

[riggi91]

Homework Statement

Superman (m = 90 kg) jumps over a 78 m tall building by first accelerating from rest to his maximum velocity in 0.004 s. Subsequent to this time, Superman follows normal projectile motion. What is the average force acting on Superman that gives his upward acceleration?. In determining the initial velocity, ignore the distance superman travels during his initial acceleration stage. Also, assume he is jumping straight up. Do not use exponential notation in submitting your answer.

Homework Equations

The equations that I have gathered are:
F=ma
A=v/t
vf^2=vi^2-2ad
vf=vi+at

The Attempt at a Solution

I know that I have to find the Initial velocity first, but in order to do so I need either Time or Acceleration, which I have neither of. All I have found is that the downward force on superman due to gravity at any given time is 882.9N.

Please guide me in the direction to get the answer! Also please don't just give me the answer as I need to learn how to do this for my Physics class!

Thanks!

 

[Simon Bridge]

But you do know the initial velocity:

Superman (m = 90 kg) jumps over a 78 m tall building by first accelerating from rest to his maximum velocity in 0.004 s

... you nee ##\sum F = ma##

 

[riggi91]

Duh! I don't know why I didnt realize that before. I also believe I've found vf

I used vf^2=vi^2-2ad and got 39.099 m/s for the vf. If that is correct would i just use a=v/t to find out a?

 

[riggi91]

I got the answer. after i found vf i used a=v/t and then just used F=ma and my answer was 879727.5N

Thank you for your help!

 

[Simon Bridge]

No worries :)