A block is attached to the end of an ideal spring and moved from coordinate $x_i$ to coordinate $x_f.$ The relaxed position is at $x=0.$ The work done by spring is positive if

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