**21.** Rohit completes a semi circular path of radius R in 10 seconds. Calculate average speed and average velocity in m/s.

**A.** \(\frac{2\pi R}{10},\frac{2R}{10}\)

**B.** \(\frac{\pi R}{10},\frac{R}{10}\)

**C.** \(\frac{\pi R}{10},\frac{2R}{10}\)

**D.** \(\frac{2\pi R}{10},\frac{R}{10}\)

**Answer :** Option C

**22.** A particle moves 4m in the south direction. Then it moves 3m in the west direction. The time taken by the particle is 2 second. What is the ratio between average speed and average velocity ?

**A.** \(\frac{5}{7}\)

**B.** \(\frac{7}{5}\)

**C.** \(\frac{14}{5}\)

**D.** \(\frac{5}{14}\)

**Answer :** Option B

**23.** A particle is projected vertically upwards with velocity 30 m/s. Find the ratio of average speed and instantaneous velocity after 6 s. \(\left [ g=10\ ms^{-2} \right ]\)

**24.** The motion of a particle along a straight line is described by the function \(x=\left ( 3t-2 \right )^{2}\). Calculate the acceleration after 10s.

**A.** \(9\ ms^{-2}\)

**B.** \(18\ ms^{-2}\)

**C.** \(36\ ms^{-2}\)

**D.** \(6\ ms^{-2}\)

**Answer :** Option B

**Explanation :**

\(v=\frac{\mathrm{d} x}{\mathrm{d} t}\) and \(a=\frac{\mathrm{d} v}{\mathrm{d} t}\)

**25.**

Given figure shows a graph at acceleration \(\rightarrow \) time for a rectilinear motion. Find averageacceleration in first 10 seconds.

**A.** \(10\ ms^{-2}\)

**B.** \(15\ ms^{-2}\)

**C.** \(7.5\ ms^{-2}\)

**D.** \(30\ ms^{-2}\)

**Answer :** Option C

**26.** A body starts its motion with zero velocity and its acceleration is \(3\ ms^{-2}\). Find the distance traveled by it in fifth second.

**27.** A body is moving in x direction with constant acceleration \(\alpha \). Find the difference of the displacement covered by it in nth second and \((n-1)^{th}\) second.

**A.** \(\alpha \)

**B.** \(\frac{\alpha }{2}\)

**C.** \(3\alpha \)

**D.** \(\frac{3\alpha }{2}\)

**Answer :** Option A

**28.** What does the speedometer measure kept in motorbike ?

**A.** Average velocity

**B.** Average speed

**C.** Instantaneous speed

**D.** Instantaneous velocity

**Answer :** Option C

**29.** The displacement of a particle in x direction is given by \(x=9-5t+4t^{2}\). Find the velocity at time \(t = 0\)

**30.** A freely falling particle covers a building of 45m height in one second. Find the height of the point from where the particle was released. \(\left [ g=10\ ms^{-2} \right ]\)