1. A bullet fired into target loses half its velocity after penetrating 25 cm . how much further will it penetrate before coming to rest ?

2. If K.E of a body increases by 0.1 % , the percent increase in its momentum will be ?

3. A postion dependent force F = ( 7 - 2x + 3x square )N acts on a small body of mass 2kgand displaces it from x = 0 to x = 5m. Work done in joule is ?

1. Well assuming that the body experiences constant retardation:
Work done by retarding force= change in kinetic energy
F.(25/100)=mv.v/4
m.a.(0.25)=m.(v^2)/4
a= -v^2 ( - gives direction )
so apply 3rd equation of motion :
we get
final velocity , v,=0
initial velocity = v/2 ( when it has penetrated 25cm)
​retardation=v^2
So0=(v.v)/4-2(v.v)S
so S=1/8 (m)

2.   Assuming mass of object to be constant, so change in momentum will be 0.031%
3. Work done by variable force = integral(algebraic sum) of all small work done by the variable 

Work done during small displacement(dW) = F.(dx).cosQ ( Q=0' as displacement is in direction of applied force )
integration with respect to x with limits 0 to 5/100 metres
W=|7x-x^2/2| ( now put x=0.05)
    =0.35-0.00125
    = 0.34875J