I don't think an object can exert a force on itself.
Try it: Get up on a skateboard, and see if you can do anything to yourself that makes you start moving ... without touching anything else.
It'll be easy to tell if you succeed. If you actually do exert an unbalanced force on yourself, then you'll begin to accelerate.
Answer:
1. B has no acceleration because the straight line shows that it's a constant speed not speeding up or down.
2. A because you can see the decline in speed as time goes on
Answer:
Explanation:
A and B are in series , Total resistance = Ra + Rb
This resistance is in parallel with single resistor C
Equivalent resistance Re = Rc x ( Ra + Rb ) / [Rc + ( Ra + Rb )]
Now this combination is in series in single resistance D .
Total resistance = Rd + Re
= Rd + { Rc x ( Ra + Rb ) / [Rc + ( Ra + Rb )] }
The equation to find force is f=ma. So, if you plug in the information that you have you'll get F=5x3 and that'll equal F=15N
