A thin strip 10 cm long is on a U shaped wire of negligible resistance and it is connected to a spring of spring constant $0.5 \mathrm{Nm}-1$ (see figure). The assembly is kept in a uniform magnetic field of 0.1 T . If the strip is pulled from its equilibrium position and released, the number of oscillations it performs before its amplitude decreases by a factor of e is N . If the mass of the strip is 50 grams, its resistance $10 \Omega$ and air drag negligible, N will be close to