Question

Assume that the earth goes round the sun in a circular orbit with a constant speed of 30 km/s. Then,

• A. The average velocity of the earth from 1st Jan, 90 to 30th June, 90 is zero
• B. The average acceleration during the above period is 60 km/s²
• 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) we can see there is a displacement from A to B .$\therefore$ average velocity cannot be zero
(b) $a_{avg}=\frac{{\overrightarrow{v}}_2-{\overrightarrow{v}}_1}{t}=\frac{30\hat{i}-(-30\hat{i})}{6months}=\frac{60}{6\times 30\times 3600}km/s^2$ which is already not 60 km/$s^2$
(c) average speed is not zero as total distance covered is not zero
(d) The instantaneous acceleration will point to the sun as the above described motion is uniform circular motion with sun at the centre of the circular path.