Hangzhou Platinum Coast Hotel

(1) Apply Newton's second law to Niu Niu: mg-0.4mg=ma 1.

Get: a 1 =6m/s 2.

Niu Niu's falling process is a uniform linear motion, which is determined by the displacement time relationship:

h 1 = 1 2 a 1 t 2

Solution: t=3s

(2) Wu Yun's accelerated movement: S= 1 2 a? 2 tons 2

Solution: a 2 =2m/s 2

From the relationship between speed and time: υ 2 =a 2 t=6m/s

(3) The falling speed of Niu Niu h 1: υ1= a1t =18m/s.

In the process of buffering, Niu Niu is determined by kinetic energy theorem.

De: W+mg h 2 =0- 1 2 m υ 1 2。

W=- 1770J

Answer: (1) The time before Niu Niu fell down was 3s;

(2) Wu Juping ran downstairs at a speed of 6m/s;

(3) The work done by Wu Juping to Niu Niu in the buffering process is-1770J.