Question

Assume that the earth goes round the sun in a circular orbit with a constant speed of ${\text{30 km s}}^{-1}$. Which of the following is correct?

• A. The average velocity of the earth from 1st Jan., 90 to 30 th June, 90 is zero.
• B. The average acceleration during the above period is $60{\text{km s}}^{-2}$.
• C. The average speed from 1st Jan., 90 to 31st Dec., 90 is zero.
• D. The instantaneous acceleration of the earth points towards the sun.

Answer 1

The correct option is D The instantaneous acceleration of the earth points towards the sun.

a)from 1st Jan., 90 to 30 th June, 90 earth completes half the revolution, so displacement is non zero. hence average velocity cannot be zero.
b) Average acceleration is change in velocity per time.
In the above time interval ( 181 days) change in velocity is $30-(-30)=60{\text{km s}}^{-1}$, So average acceleration is $\frac{60}{181\times 24}{\text{km s}}^{-2}$
c) As the particle is under motion average speed is never zero d)Since the speed is given to be constant therefore there is no tangential acceleration, net acceleration points towards centre of revolution ie sun.