An object 'O' is placed at a distance of $$100 \mathrm{~cm}$$ in front of a concave mirror of radius of curvature $$200 \mathrm{~cm}$$ as shown in the figure. The object starts moving towards the mirror at a speed $$2 \mathrm{~cm} / \mathrm{s}$$. The position of the image from the mirror after $$10 \mathrm{~s}$$ will be at _________ $$\mathrm{cm}$$.

In an experiment with a convex lens, The plot of the image distance $$\left(v^{\prime}\right)$$ against the object distance ($$\left.\mu^{\prime}\right)$$ measured from the focus gives a curve $$v^{\prime} \mu^{\prime}=225$$. If all the distances are measured in $$\mathrm{cm}$$. The magnitude of the focal length of the lens is ___________ cm.

In an experiment to find acceleration due to gravity (g) using simple pendulum, time period of $$0.5 \mathrm{~s}$$ is measured from time of 100 oscillation with a watch of $$1 \mathrm{~s}$$ resolution. If measured value of length is $$10 \mathrm{~cm}$$ known to $$1 \mathrm{~mm}$$ accuracy, The accuracy in the determination of $$\mathrm{g}$$ is found to be $$x \%$$. The value of $$x$$ is ___________.