Question

a is 5 m/s square ,distance is8.4 m,and v is 10m ,find u

Answer 1

a= 5m/s^2
s= 8.4m
v= 10m/s
u=?
by the equation of motion
2as= v^2-u^2
2*5*8.4= (10)^2- u^2
84= 100-u^2
u^2= 100/84
u^2= 1.19
u= √1.19m/s.

Answer 2

From the 3rd eq. of motion, we have
$v^{2} - u^{2} = 2as$
$(10)^{2} - u^{2} = 2 \times 5 \times 8.4 \\ 100 - u^{2} = 84 \\ 100 - 84 = u^{2} \\ 16 = u^{2} \\ \sqrt{16} = u$
4m/s=u