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Question 12 Marks
A cyclist starts from centre O of a circular park of radius 1km and moves along the path OPRQO as shown Fig. If he maintains constant speed of $10ms^{–1}$, what is his acceleration at point R in magnitude and direction?

 
Answer
The path of the cyclist at R is circular of constant radius 1km with centre O and he is moving with constant speed 10m/ s. So his motion is uniform circular motion at R.

Hence, the R = 1000m, v =10m/ s

$\therefore\ \text{a}_\text{c}=\frac{\text{v}^2}{\text{R}}=\frac{10\times10}{1000}=\frac{1}{10}=0.1\text{m/ s}^2$ along RO.
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Question 22 Marks
A, B and C are three non-collinear, non co-planar vectors. What can you say about direction of A × (B × C)?
Answer
The direction of the vector $(\vec{\text{B}}\times\vec{\text{C}})$ will be perpendicular to the plane containing by vectors $\vec{\text{B}}$ and $\vec{\text{C}}$ by Right-hand thumb or Right-hand grip rule (RHGR).

The direction of the vector $\vec{\text{A}}\times(\vec{\text{B}}\times\vec{\text{C}})$ will be perpendicular to $\vec{\text{A}}$ and in a plane containing $\vec{\text{B}}$ and $\vec{\text{C}}$ by Right-hand grip rule.
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