[Spoiler] AAMC SB Physics #89

After a block began to slide, how did the speed vary over time?

A) It was constant in time B) It increased exponentially with time C) It was constant at first, then increased linearly D) It increased linearly with time.

The correct answer is D.

But why isn't it B? Since it asks for the speed, wouldn't it be exponentially? Because the acceleration is linear, then the velocity would be linear. Even the AAMC explanation says there is a net accelerating force on the block once it slides

P.S. This is a passage question, where the block on a table and is attached to a mass that is hanging off the table (Block is not stationary)