1. The problem statement, all variables and given/known data Two equal and opposite charged objects of magnitude 2C and mass 2kg are attached to a spring of spring constant 4 N/m in the natural length of the spring. The system is suddenly placed in a uniform electric field of field strength 5 N/C in the direction of electric field such that the -ve charge is towards the origin of electric field. assuming the natural length of the spring to be large, find the maximum compression and elongation in the spring length. 2. Relevant equations 3. The attempt at a solution First I tried to find the maximum extension. Let charge -2 C be at a distance x1 and charge +2 be at a distance x2 from the origin . Let the length of the spring be l . The length of the spring at any instant is x2-x1 . The extension in the spring would be x2-x1-l . The force of attraction between the charges would be kq2/(x2-x1)2 i.e 16/(x2-x1)2 Force due to the external electric field will be of magnitude 10N . EOM for mass 1 (i.e -2C ) will be k(x2-x1-l)-10+16/(x2-x1)2 = 2d2x1/dt2 EOM for mass 2 (i.e +2C ) will be 10-k(x2-x1-l)-16/(x2-x1)2 = 2d2x2/dt2 From the above we get , 2(d2x2/dt2-d2x1/dt2)=20-2k(x2-x1-l)-32/(x2-x1)2 or , d2x2/dt2-d2x1/dt2=10-k(x2-x1-l)-16/(x2-x1)2 d2(x2-x1)/dt2=10-k(x2-x1-l)-16/(x2-x1)2 Now putting x2-x1 = z , We have d2z/dt2=10-k(z-l)-16/z2 .Now I need to maximize z . Is it the correct way to approach the problem ? I would be grateful if someone could help me with the problem .