A) \[60\text{ }m/s,\text{ }40\text{ }m/{{s}^{2}}\]
B) \[70\text{ }m/s,\text{ }30\text{ }m/{{s}^{2}}\]
C) \[90\text{ }m/s,\text{ }60\text{ }m/{{s}^{2}}\]
D) None of the above
Correct Answer: C
Solution :
Since, \[{{S}_{nth}}=u+\frac{1}{2}f(2n-1)\] \[\therefore \] \[{{S}_{11th}}=u+\frac{1}{2}f(21)=720\] ?..(i) and \[{{S}_{15th}}=u+\frac{1}{2}f(29)=960\] ?.(ii) On subtracting Eq. (ii) from Eq. (i), we get \[4f=240\] \[\Rightarrow \] \[f=60\] \[\therefore \] From Eq. (i), \[u+\frac{1}{2}\,(60)\,(21)=720\] \[\therefore \] \[u=720-630=90\] Hence, \[u=90\,m/s\] \[f=60m/{{s}^{2}}\]
You need to login to perform this action.
You will be redirected in
3 sec
