Self Evaluation Test

Give at least two illustrations of Newton's third law of motion.

The blades of a ceiling fan continue to rotate even when the current is switched off. Why?

Two bodies on the surface of the earth do not move towards each other due to force of attraction given by Newton's law of gravitation. Why?

A constant retarding force of $40 \mathrm{N}$ is applied to the body of mass $20 \mathrm{kg}$ moving initially with a speed of $14 \mathrm{m} {\mathrm{s}}^{-1}$. How long does the body take to stop in seconds?

A ball is thrown vertically upward from the top of a cliff of height $21.21 \mathrm{m}$ with an initial velocity $11 \mathrm{m}/\mathrm{s}$. Taking $\mathrm{g}=9.8 \mathrm{m}/{\mathrm{s}}^2$, calculate the height (in $\mathrm{m}$) to which it will rise before returning to the ground. (Find the value upto two decimals.)

A ball is thrown vertically upward from the top of a cliff of height $21.21 \mathrm{m}$ with an initial velocity $11 \mathrm{m}/\mathrm{s}$. Taking $\mathrm{g}=9.8 \mathrm{m}/{\mathrm{s}}^2$, calculate the velocity with which it will strike the ground in terms of metre per second.
Choose correct answer from the given options $(23.16, 30)$

A ball is thrown vertically upward from the top of a cliff of height $21.21 \mathrm{m}$ with an initial velocity $11 {\mathrm{ms}}^{-1}$ and while coming down its velocity is $23.16 {\mathrm{ms}}^{-1}$. Taking $\mathrm{g}=9.8 {\mathrm{ms}}^{-2}$, calculate the total time of the journey of the ball in seconds.

A spherical body of mass $60 \mathrm{kg}$ attract a body of mass $40 \mathrm{kg}$ with a force equal to $4\times {10}^5 \mathrm{N}$. Calculate the distance between them in metres. Take $\mathrm{G}=6\times {10}^{-11} {\mathrm{Nm}}^{2 }{\mathrm{kg}}^{-2}$ and acceleration due to gravity $\left(\mathrm{g}\right)=10 {\mathrm{ms}}^{-2}$.