Question

an object with a mass of 10kg moves at a constant velocity of 10m/s. A constant force then acts for 4 sec on the object and gives it a speed of 2m/sec in opposite direction. The force acting on the object is

Answer 1

Change in velocity 
-2-10=-12
Time required is 4 seconds 
a=Δv/t
=-12/4
=-3 m/s²