有3个网友回答
1.加速度为a=2*3/1^2=6
第n秒内的位移s=1/2*6*n^2-1/2*6*(n-1)^2=3n^2-3(n-1)^2 =3(2n-1)
n秒末速度为v=6*n=6n
2.设加速度为a,斜面长为L,走完斜面上半部分的时间为t1,走完全部的时间t2
t1=根号[2*L/2)/a]=根号(L/a)
t2=根号[2*L)/a]=根号(2L/a)
下半部分用的时间为 t3=t2-t1=根号(2L/a)-根号(L/a)
则n=t3/t1=[根号(2L/a)-根号(L/a)]/根号(L/a)=根号2-1
3.加速度为a=2*4/2^2=8/4=2
4.(1)设加速度为a,
1/2*a*3^2+3a*2=14
解得a=4/3
(2.)物体匀速运动的位移s=3*4/3*2=8m
5.第1秒内的位移为 s1=1/2*a*1^2=a/2
第10秒内的位移为 s2=1/2*a*10^2-1/2*a*9^2==19a/2
在第10s内的位移和在第1s内的位移之比为
s2/s1=(19a/2)/(a/2)=19:1
6.设杆全部通过A需用的时间为t
15+5=1/2*10*t^2
t=根号(2*20/10)=2s
1.第一秒走了3m。S=0.5×a×t^2 a=6
第N秒 Sn-S(n-1)
=0.5×6n^2 -3×(n-1)^2
=6n-3
n秒末速度V=at=6t
2.下一半时间为上一半时间的n倍,则总过程是上一半的n+1倍
由S=0.5×a×t^2得
S总/S1 n=根号2 减去1
3.S=0.5×a×t^2
4=0.5×a×2^2
a=2m/s^2
4.加速过程:S=0.5×a×t^2
V=at
匀速运动:S2=V(t2)
S+S2=14m
t=3 t2=2
解得:a=4/3 S2=8m
5.S=0.5×10×t^2
第n秒位移是 Sn-S(n-1)=5×(2n-1)
第一秒位移S1=5 第十秒S10=95
S10/S1=19
6.S=0.5×a×t^2
竿下端到达A点时,下端通过位移是5m
t1=1s
竿上端到达A点时,下端通过位移是20m
t2=2秒
2-1=1
所以通过A点需要1秒
1 3(2n-1) 6n (每秒内位移之比是1:3:5:7... a=6m/s2)
2 根号2-1 (末速度是1,中距离点速度为 根号2/2, 时间比就是速度的变化之比)
3 2m/s2 (s=1/2at^2)
4 设末速度为Vt
14=1/2*Vt*T1+Vt*T2 Vt=4m/s
a=4/3 m/s2
S2=4*2=8m
5 19:1 (同第一题)
6 1/2*g*t^2=15+5 t=2s
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