问题 选择题

某星球的质量约为地球质量的9倍,半径约为地球半径的一半,若从地球表面高h处平抛一物体,射程为60m,则在该星球上,从同样高度以同样的初速度平抛同一物体,射程应为(  )

A.10 m

B.15 m

C.90 m

D.360 m

答案

设星球质量为M′,半径为R′,地球质量为M,半径为R.

已知:

M′
M
=9,
R′
R
=
1
2

根据万有引力等于重力得:G

Mm
R2
=mg

g=G

M
R2

所以:

g
g′
=
MR′2
M′R2
=
1
36
…①

由题意从同样高度抛出:h=

1
2
gt2=
1
2
g′t′2…②

①、②联立,解得:t′=

1
6
t

在地球上的水平位移:s=v0t=60m,在星球上的水平位移:s′=v0t′=

1
6
v0t=10m

故选A.

单项选择题
单项选择题

All her life, my mother wanted busy children. It was very important that her house should remain at all times clean and tidy.

You could turn your back for a moment in my mother’s house, leave a half written letter on the dining table, a magazine open on the chair, and turn around to find that my mother had "put it back where it belonged," as she explained. My wife, on one of her first visits to my mother’s house, placed a packet of biscuits on an end table and went to the kitchen to fetch a drink. When she returned, she found the packet had been removed. Confused, she set down her drink and went back to the kitchen for more biscuits, only to return to find that her drink had disappeared. Up to then she had guessed that everyone in my family held onto their drinks so as not to make water rings on the end tables. Now she knows better.

These disappearances had a confusing effect on our family. We were all inclined to forgetfulness, and it was common for one of us, upon returning from the bathroom, to find the every sign of his work in progress had disappeared suddenly. "Do you remember what I was doing" was a question frequently asked, but rarely answered.

Now my sister has developed a secondhand love of clean windows, and my brother does the cleaning in his house, perhaps to avoid having to be the one to lift his feet. I try not to think about it too much, but I have at this later time started to dust the furniture once a week.

This passage mainly tells us that()

A.my mother often made us confused

B.my family members had a poor memory

C.my mother helped us to form a good habit

D.my wife was surprised when she visited my mother