CBSE Class 8 Physics (Demo)

A robot runs forward with $$5 \mathrm{~m} \mathrm{~s}^{-1}$$ for 10 s and immediately backwards with $$5 \mathrm{~m} \mathrm{~s}^{-1}$$ for 5 s . Which of the following statements is wrong?

A train travels with a speed of $$100 \mathrm{~km} \mathrm{~h}^{-1}$$ towards north for $$1 \frac{1}{2} \mathrm{~h}$$, the distance covered by the train is $$\qquad$$ km

Assertion (A): The average speed of a bus moving in a straight path is equal to its average velocity.
Reason (R): Average speed $$=\frac{\text { Total displacement }}{\text { Total time }}$$

Assertion (A): The time period of a simple pendulum of length $$(\ell)$$ is less on the earth than on the moon.
Reason ( $$\mathbf{R}$$ ): The value of acceleration due to gravity on the earth is six times the acceleration due to gravity on the moon.

Match the statements of Column $$A$$ with those of Column B.

Write the following steps in sequence to determine the time period of a simple pendulum.
(A) Start the stopwatch when the bob is at the mean or extreme position and find the time taken by the pendulum to complete 20 oscillations.
(B) Take a simple pendulum of length $$(\ell)$$ and a stopwatch.
(C) Move the bob of the pendulum to one side and release it.
(D) Divide the time taken for 20 oscillations by 20 and obtain the time period $$(T)$$ of the simple pendulum.

Write the following steps in sequence to find the average speed of a ball rolled on a floor.
(A) Take a ball, measuring tape and a stopwatch.
(B) Note the time taken by the ball to come to halt.
(C) Roll the ball on the floor and at same instant start the stop watch.
(D) Measure the distance with the help of the measuring tape.
(E) The average speed of the ball is the ratio of total distance travelled by ball to the total time taken.

Which among the following sentences is correct?

Most of the amount of heat energy flows from the bottom layers of air to the top in a room fitted with AC through

Assertion (A): Temperature of a body can be increased by passing sound waves through it.
Reason ( $$\mathbf{R}$$ ): Heat and sound are different forms of energy.

Assertion: Convection is the process of transfer of heat energy in metals.

Reason: The atoms in metals are not free to move from one place to another.

Which among the following can be the temperature of water?

Which among the following temperature can be measured using a mercury thermometer?

The space between the walls of a thermos flask is kept vacuum. This is to prevent:

Arrange the following process in the increasing order of the heat required.
(A) 100 g of ice at $$-5^{\circ} \mathrm{C}$$ to convert to water at $$100^{\circ} \mathrm{C}$$.
(B) 100 g ice at $$0^{\circ} \mathrm{C}$$ to convert to water at $$100^{\circ} \mathrm{C}$$.
(C) 100 g of water at $$0^{\circ} \mathrm{C}$$ to water at $$100^{\circ} \mathrm{C}$$.
(D) 100 g of water at $$20^{\circ} \mathrm{C}$$ water at $$100^{\circ} \mathrm{C}$$.

Which of the following is the SI unit of heat?

Match the entries of Column A with those of Column B.