A spring of natural length $L$ compressed to length $\frac{7L}{8}$ exerts a force $F_0.$ The work done by the spring in restoring itself to natural length is

The $300 \mathrm{N}$ crate slides down the inclined curved path from $A$ to $B$ in the vertical plane as shown in the figure. If the crate has a velocity of $1.2 \mathrm{m} {\mathrm{s}}^{–1}$ down the inclined at point $A$ and $8 \mathrm{m} {\mathrm{s}}^{–1}$ at $B.$ Find the work done against friction during the motion.

For a block of mass $m$ to slide without friction up the rise of height $h$ shown, it must have a minimum initial speed of