Physics
posted by Ron .
A v vs t graph is drawn for a ball moving in one direction. The graph starts at the origin and at t=5s the acceleration of the ball is zero. We know that at t=5s,
a) the curve is not crossing the time axis
b) the velocity of the ball is not changing
c) the slope of the curve is nonzero
d) the curve is at v=0, t=0

I assume you know that when the acceleration is zero, the velocity is not changing

i think b is correct.. but what makes "a" incorrect?

When t=5, you are not crossing the velocity (vertical) axis. If you were crossing the time axis, the velocity would be zero.
It is not impossible for velocity and acceleration to be zero at the same time, asymptotically. But if you are crossing the time axis, velocity must be changing with time. If acceleration is zero, you are not crossing the time line. So I agree (a) is OK also 
but there is only one correct answer

Not this time. Flip a coin