Answer:
Average recoil force experienced by machine will be 200 N
Explanation:
We have give mass of each bullet m = 50 gram = 0.05 kg
There are 4 bullets
So mass of 4 bullets = 4×0.05 = 0.2 kg
Initial speed of the bullet u = 0 m/sec
And final speed of the bullet v = 1000 m/sec
So change in momentum 
Time is given per second so t = 1 sec
We know that force is equal to rate of change of momentum
So force will be equal to 
So average recoil force experienced by machine will be 200 N
The equivalent resistance of n resistors in series is given by:

In our circuit, we have three resistors of

each, therefore the equivalent resistance of the circuit is
The power of a machine is the work/time ratio for that particular machine
Its the rate of doing work.
Answer:
The work done by this force can be found via the following formula

Explanation:
Alternatively, the work done by the object is equal to the elastic potantial energy done by the spring.
