$8.$ We would use shearing to cut a whole rectangle section of a work piece with length $200$mm$,$

width $25$ mm$,$ thickness $5$mm$.$ Please $1)$ calculate the shear force $(2$ points$),2)$ the required

shearing work $($energy$)(2$ points$).$ The metal's shear strength $=500$ MPa, and the penetration

requires $20\%$ of thickness.