What is the net force

A 2.4 kg otter starts from rest at the top of a
muddy incline 89.8 cm long and slides down
to the bottom in 0.40 s.
What net external force acts on the otter
along the incline?
Answer in units of N

The net force f = mA; so we find A the acceleration down the mud.

Vavg = S/T = .898/.4 = (U + V)/2 = AT/2 when U = 0; so that A = 2S/T^2 and f = mA = 2.4*2*.898/.4^2 = 26.94 Newtons ANS.