$A$ car moves with a speed of $20 \, m/s$ towards the North. It turns and moves with the same speed towards the West. What is the change in velocity?

Two forces of magnitude $8 \, N$ and $15 \, N$ respectively act at a point. If the resultant force is $17 \, N$,the angle between the forces is: (in $^{\circ}$)

Four forces act on a stationary particle at the origin of a coordinate system: $\overrightarrow{F_1} = 3\hat{i} - \hat{j} + 9\hat{k}$,$\overrightarrow{F_2} = 2\hat{i} - 2\hat{j} + 16\hat{k}$,$\overrightarrow{F_3} = 9\hat{i} + \hat{j} + 18\hat{k}$,and $\overrightarrow{F_4} = \hat{i} + 2\hat{j} - 18\hat{k}$. In which plane will the particle move under the influence of these forces?

Two forces $3\,N$ and $2\,N$ are at an angle $\theta$ such that the resultant is $R$. The first force is now increased to $6\,N$ and the resultant becomes $2R$. The value of $\theta$ is ....... $^\circ$.

$A$ truck travelling due north at $20 \, m/s$ turns west and travels at the same speed. The change in its velocity is

Two forces,each of magnitude $F$,have a resultant of the same magnitude $F$. The angle between the two forces is....... $^o$