匀质圆盘半径为R,质量为m,沿斜面作纯滚动。已知轮心加速度为a,则圆盘个质点的惯性力向O点简化的结果是:惯性力系主矢的大小等于(  )。

A、<img src="https://s3.cn-north-1.amazonaws.com.cn/qingshuxuetang/examination/imgUplod/15234952260994406310153244ee19eb6101fac2ad626image48.jpeg">

B、<img src="https://s3.cn-north-1.amazonaws.com.cn/qingshuxuetang/examination/imgUplod/15234952263713f512251a48748508a4671bf72e577e1image49.jpeg">

C、<img src="https://s3.cn-north-1.amazonaws.com.cn/qingshuxuetang/examination/imgUplod/152349522646489421dfbdb854d80bb3df4cde92c56c8image50.jpeg">