L = 100;
H = 50;
D = sqrt(L*L-H*H);
k = 10;


dH = -30:0.1:130;

Fk = k * (L - sqrt((H-dH).^2+D^2));
F = 2 * Fk .* (H-dH) ./ sqrt((H-dH).^2+D^2);

plot(dH,F); grid on; 