The picture shows all of my work:)
Answer:

Explanation:
The force experimented by a charge <em>q </em>in a uniform electric field <em>E</em><em> </em>is <em>F=qE</em>.
Newton's 2nd Law tells us that the relation between acceleration <em>a</em> a mass <em>m </em>experiments when a force <em>F </em>is applied to it is <em>F=ma</em>.
Combining these equations we have <em>am=qE</em>, and since we want the acceleration of the speck of dust, we substitute our values:

Answer:
a. when the acceleration of the objects become negative
Answer:
its velocity is 51, or 51.42 to be exact it would be: 51.4285714286