Answer:
0 m/sec
Explanation:
b/c they were at rest and initial means at rest ,at rest means 0 HOPE THIS HELPS
(2nd variant, 7kg is 3 times faster than 21kg)
It's always a good idea to start with the definition of the thing you're trying to find.
This problem is just trying to find out whether you KNOW the definition of acceleration. You may know it, but you haven't used it yet.
Average acceleration = (change in velocity) divided by (total time).
Change in velocity = (end value) minus (start value)
Change in velocity = (20m/s) - 0
Change in velocity = 20 m/s
Time = 10 s
Average acceleration = (20m/s)/(10s)
Average acceleration = 2 m/s^2