[填空题]
The motion of an object released from a high place in a vacuum is observed. The variation of its velocity with time is recorded and the following graph is obtained.
1.Discuss the role that observations play in the development of scientific understanding.
2.Other than velocity and time, list two quantities that can be obtained from the graph.
3.(1)The height of the release point is 70 m. Show that the speed $v_1$ of the object just before the contact with the ground is $37\,m\,s^{−1}$. $v_1$ = $m\,s^{-1}$
(2)The object rebounds from the ground with a speed $v_2$ of $17\,m\,s^{−1}$. The mass of the object is 8.0 kg and the contact time during the rebound is 0.50 s. $F_N$ = N
Calculate the average force acting on the object from the ground.
