Calculating force from distance traveled and initial speed of projectile

[Felchi]

Homework Statement

Estimate the average force exerted by a shot-putter on a 7.0-kg shot if the shot is moved through a distance of 3.0m and is released with a speed of 10m/s .

Homework Equations

F=ma
Maybe the Five Equations for constant acceleration?

The Attempt at a Solution

So my guess is that I need to find acceleration. I tried:

v_f^2=v_i^2+2ad
0^2=10m/s^2+2(a)3m
0=100 m^2/s^2+6m(a)
(-100 m^2/s^2)/6m=a
16.67m/s^2=a

So
F=7kg*16.67m/s^2
F=116.67

But I was told this is wrong

 

[Mark44]

Homework Statement

Estimate the average force exerted by a shot-putter on a 7.0-kg shot if the shot is moved through a distance of 3.0m and is released with a speed of 10m/s .

Homework Equations

F=ma
Maybe the Five Equations for constant acceleration?

The Attempt at a Solution

So my guess is that I need to find acceleration. I tried:

v_f^2=v_i^2+2ad
0^2=10m/s^2+2(a)3m
0=100 m^2/s^2+6m(a)
(-100 m^2/s^2)/6m=a
16.67m/s^2=a

So
F=7kg*16.67m/s^2
F=116.67

But I was told this is wrong

The key to this question, I believe, is the phrase "average force," which is the change in momentum divided by the elapsed time.
$$\bar{F} = \frac{m(v_f - v_i)}{\Delta t}$$