If one rushes to join the ruku so they catch that particular rak’ah, then this is not permissible. The Holy Prophet^(sa) said:

 إِذَا أُقِيمَتِ الصَّلاَةُ فَلاَ تَأْتُوهَا وَأَنْتُمْ تَسْعَوْنَ وَلَكِنِ ائْتُوهَا وَأَنْتُمْ تَمْشُونَ وَعَلَيْكُمُ السَّكِينَةُ فَمَا أَدْرَكْتُمْ فَصَلُّوا وَمَا فَاتَكُمْ فَأَتِمُّوا

“When the Iqamah is called for Salat do not come to it rushing, rather come to it walking, and while you have tranquillity. What you catch of it then pray it, and what you missed of it, then complete it.” (Jami at-Tirmidhi, The Book on Salat, What Has Been Related About Walking To The Masjid)