问题 问答题

冰壶由花岗岩凿磨而成,质量为20kg,与冰道接触的底面积约为200cm2,冰壶的体积为8×10-3m3,则这种花岗岩的密度为多少?冰壶停在水平冰面上时对冰面的压强为多少?(g取10N/kg)

答案

(1)这种花岗岩的密度:

ρ=

m
V
=
20kg
8×10-3m3
=2.5×103kg/m3

(2)冰壶停在冰面上时,对冰面的压力:

F=G=mg=20kg×10N/kg=200N,

对冰面的压强:

p=

F
S
=
200N
200×10-4m2
=1×104Pa.

答:这种花岗岩的密度为2.5×103kg/m3,冰壶停在水平冰面上时对冰面的压强为1×104Pa.

名词解释
单项选择题

I was a single parent of four small children, working at a low paid job. Money was always tight, but we had a (1) over our heads, food on the table, clothes on our backs, and if not a lot, always (2) . Not knowing we were poor, my kids just thought I was (3) . I’ve always been glad about that.

It was Christmas time, and although there wasn’t (4) for a lot of gifts, we planned to celebrate with a family party. But the big (5) for the kids was the fun of Christmas (6) .

They planned weeks ahead of time, asking (7) what they wanted for Christmas. Fortunately, I had saved MYM120 for (8) to share by all five of us.

The big (9) arrived. I gave each kid a twenty-dollar bill and (10) them to look for gifts of about four dollars each. Then everyone scattered. We had two hours to shop; then we would (11) back at the "Santa’s Workshop".

Driving home, everyone was in high Christmas spirits, (12) my younger daughter, Ginger, who was unusually (13) . She had only one small, flat bag with a few candies—fiftycent candies! I was so angry, but I didn’t say anything (14) we got home. I called her into my bedroom and closed the door, (15) to be angry again. This is what she told me.

"I was looking (16) thinking of what to buy, and I (17) to read the little cards on the ’Giving Trees’. One was for a little girl, four years old, and all she (18) for Christmas was a doll. So I took the card off the tree and (19) the doll for her. We have so much and she doesn’t have anything. "

I never felt so (20) as I did that day.

8()

A.toys 

B.clothes 

C.presents 

D.bills