Question

When dropping a knife straight down into a jar of peanut butter should the acceleration be larger than gravitational acceleration? Should the knife have sped up more rapidly than it slowed down, or the reverse?

Answer 1

When a knife is dropped straight down into a jar of peanut butter, the acceleration is usually larger than the gravitational acceleration. This is because resistive force or viscous force due to the peanut butter is larger than the gravitational force on the knife. This can be easily noticed because the change in velocity-squared

for a given distance traveled in air by the knife is more than that in the peanut butter.

No it is the reverse, it actually, slowed down more rapidly than speeding up in the air.