Traditional Culture Encyclopedia - Photography and portraiture - Huaian 3D photography

Huaian 3D photography

Let the thickness of each brick be d and 9d-3d=aT2① when moving up.

When moving down: 3d-d=a'T2②

Simultaneous ① ②: AA ′ = 31③

According to Newton's second law, when moving upwards: mg+f = ma4.

When moving downward: mg-f=ma'⑤

Simultaneous 34 ⑤: f =12 mg;

Therefore, choose: B.