Work And Energy — Science STD 9 — Question

A boy of mass 50kg standing on ground exerts a force of 500N on the ground. The force exerted by the ground on the boy will be:

Isotopes of an element have:

Cell inclusions are:

Cartilage is not found in:

A person standing between two vertical cliffs and 640m away from the nearest cliff shouted. He heard the first echo after 4 seconds and the second echo 3 seconds later. What is the distance between the cliffs?

The element having atomicity ‘four’ is most likely to be:

1. Argon.
2. Fluorine.
3. Phosphorus.
4. Francium.

The energy absorbed by a solar panal is used to charge a battery. During the day, the battery stores 1.6J of energy each second. At night the battery is used to light a 1.2W lamp for 18000s.
What is the minimum time for which the battery must be charged within the day?

The growing of ____ crops on a piece of land in a pre-planned succession is known as crop rotation:

Which of the following frequency of sound can be generated by a vibrating simple pendulum as well as by the vibrating vocal cords of a rhinoceros?

1. 5kHz
2. 25Hz
3. 10Hz
4. 15,000Hz

In the bell jar experiment, as air is removed from the jar: