Thời gian để ô tô đạt đc vận tốc 2m/s:

Ta có: \(v=v_0+at\Leftrightarrow t=\dfrac{v-v_0}{a}=\dfrac{2-0}{1}=2\left(s\right)\)

4.A

5.D

Ta có: \(\left\{{}\begin{matrix}p+e+n=36\\p=e\\p+e-n=12\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}2p+n=36\\p=e\\2n=24\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}p=e=12\\n=12\end{matrix}\right.\)

  ⇒ Đây là magie (Mg)

Ta có: \(\left\{{}\begin{matrix}p+e+n=24\\p=e\\n=33,33\%\left(p+e+n\right)\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}p=e=8\\n=8\end{matrix}\right.\Rightarrow z=p=e=8\)

ĐK: \(x\ge1\)

Ta có: \(\sqrt{x^2+6x+9}=x-1\)

      \(\Leftrightarrow x^2+6x+9=x^2-2x+1\)

      \(\Leftrightarrow8x=-8\Leftrightarrow x=-1\left(loại\right)\)

 ⇒ ptvn

Điền vào dấu 3 chấm là số 0 nhé

 \(M_{KNO_3}=39+14+3.16=101\left(đvC\right)\)

\(\Rightarrow m_{KNO_3}=101.\dfrac{1}{12}.1,9926.10^{-23}=1,677105.10^{-22}\left(g\right)\)

\(m_O=1,6605.10^{-24}.16=2,6568.10^{-23}\left(g\right)\)

\(m_{Al}=1,6605.10^{-24}.27=4,48335.10^{-23}\left(g\right)\)

\(m_{Fe}=1,6605.10^{-24}.56=9,2988.10^{-23}\left(g\right)\)

\(m_S=1,6605.10^{-24}.32=5,3136.10^{-23}\left(g\right)\)

Ta có: \(\left\{{}\begin{matrix}p+e+n=115\\p=e\\p+e-n=25\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}2n=90\\p=e\\2p+n=115\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}p=e=35\\n=45\end{matrix}\right.\)

     \(\Rightarrow A=p+n=35+45=80\left(u\right)\)

\(KHNT:^{80}_{35}Br\)

Lấy g = 10m/s² 

Thời gian vật chạm đất:

Ta có:\(s=\dfrac{1}{2}gt^2\Leftrightarrow t=\sqrt{\dfrac{2s}{g}}=\sqrt{\dfrac{2.100}{10}}=2\sqrt{5}\approx4,47\left(s\right)\)

Vận tốc khi vật chạm đất:

 \(v=gt=10.2\sqrt{5}=20\sqrt{5}\approx44,72\left(m/s\right)\)