解题思路:
⑴车架最轻,应采用碳纤维
质量:
m
=
ρ
V
=
2.5
×
10
—
3
m
3
×
1.6
×
103
k
g
/
m
3
=
4
kg
,
⑵
∵
匀速行驶
∴
运动员动力
F
=
F
f
=
120
N
做功:
W
=
"
F
s
=
120
N
"
×
500
m
=
6
×
10
4
J
,
功率:
1.2
×
10
3
W
⑶对地面压力:
F
‘=
G
总
=
600
N
受力面积:
S
=
2
×
40
c
m
2
=
80
c
m
2
=
8
×
10
−
3
m
2
压强:
=
7.5
×
10
4
P
a
(1)4kg,(2)1.2×10 3W,(3)7.5×10 4Pa
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