The initial speed of a body is 2.98 m/s. What is its speed after 1.6 s if it accelerates uniformly at 2.51 m/s^2?

Answer in units of m/s

What is its speed after 1.6 s if it accelerates uniformly at - 2.51 m/s^2?

Answer in units of m/s

Not sure if you are saying the acceleration is positive or negative?

The equation you would use would be v=u+at, where v=final velocity u=initial velocity a=acceleration t=time. Using this if the acceleration is 2.51m/s^2:

v=2.98 + (2.51*1.6)

v=6.996m/s

If the acceleration is - 2.51 m/s^2:

v=2.98 + (2.51*1.6)

v=-1.036m/s

V (ending) = at + v (initial)

V = (-2.51) (1.6) + 2.98

V = - 1.036 m/s

V (using significant figures) = - 1.0 m/s