I see one specific problem with your code, and a couple potential ones. To help myself see what's going on, I rewrote your code, using parameters instead of inserting repeated numbers into the equation:
t = 0:0.05:.35;
c1 = 0.0035;
c2 = 0.0335;
c3 = 0.035;
a = 1440;
g = 9.81;
b = 0.0018;
d = 2700;
v = sqrt(c1*a*g/b) * tanh(sqrt(c2*a*g*b)/(c3*d).*t);
Notice that I changed v(t) to just v. You are not making a function here, but instead are calculating values of v. [That was probably giving you a syntax error.]
One thing I notice that I find likely to be an typo on your part is that your equation has the three different values that I called c1, c2, c3. Are any of those typos?
