If the position vector of a particle is

$\vec r =  - \cos \,t\hat i + \sin \,t\hat j - 18\,t\hat k$

then what is the magnitude of its acceleration ?

  • A

    $0$

  • B

    $1$

  • C

    $sin^2\,t$

  • D

    $cos\,t$

Similar Questions

$Assertion$ : A tennis ball bounces higher on hills than in plains.
$Reason$ : Acceleration due to gravity on the hill is greater than that on the surface of earth

  • [AIIMS 2009]

Two projectiles are thrown simultaneously in the same plane from the same point. If their velocities are $v_1$ and $v_2$ at angles $\theta _1$ and $\theta_2$ respectively from the horizontal, then answer the following question

The trajectory of particle $1$ with respect to particle $2$ will be

In the figure shown, the two projectiles are fired simultaneously. The minimum distance between them during their flight is  ........ $m$

A rigid rod is sliding. At some instant position of the rod is as shown in the figure. End $A$ has constant velocity $v_0$. At $t = 0, y = l$ . 

A particle starts from the origin at $t=0$ $s$ with a velocity of $10.0 \hat{ j } \;m / s$ and moves in the $x-y$ plane with a constant acceleration of $(8.0 \hat{ i }+2.0 \hat{ j }) \;m \,s ^{-2} .$

$(a)$ At what time is the $x$ - coordinate of the particle $16\; m ?$ What is the $y$ -coordinate of the particle at that time?

$(b)$ What is the speed of the particle at the time?