A particle when projected in vertical planc moves along the fixed smooth surfacc with initial velocity $20 \mathrm{~m} / \mathrm{s}$ at an angle of $60^{\circ}$, so that its normal reaction on the surlace remains isro throughout the motion. Then find the slope of the tangent to the surface at height $5 \mathrm{~m}$ from the point of projoction $A$.