Which one is easy to hold in hand, a glass sheet or a cardboard? give reason

Opaque materials are those objects which does not allow light to pass through them. Example: - Wooden board, umbrella.

Transparent materials are those objects which allow light to pass through them in straight lines. As a result we can see the objects clearly. Example: - Plane mirror, water.

Translucent materials are those which let some light to pass through them, the light rays get scatter in all directions, so cannot see clearly through them. Example: - Fog, smoke.

Luminous objects are those which emit light on their own. Example:-Sun, firefly.

Non-luminous objects are those which reflect the light from luminous bodies. Example: - Moon, mirror.

Based on the above definitions we can classify the objects as opaque, transparent, translucent, luminous and non-luminous.

Opaque:  A piece of rock, a sheet of aluminium, a mirror, a wooden board, a CD, an umbrella, a wall, a sheet of carbon paper,  a sheet of cardboard.

Transparent: Air, water, a sheet of plane glass.

Translucent: A sheet of polythene, smoke, fog, a sheet of cellophane, a wire mesh.

Luminous: A piece of red hot iron, a lighted fluorescent tube, the flame of a gas burner, a lighted torch, sun, firefly, kerosene stove.

Non – luminous: Air, water, a piece of rock, a sheet of aluminium, a mirror, a wooden  board, a sheet of polythene, a CD, smoke, a sheet of plane glass, fog, an umbrella, a wall, a sheet of carbon paper, a sheet of cardboard, a sheet of cellophane, a wire mesh, kerosene stove, moon.

the box does not move because you need to use a force greater than 300 n. you are only using 50 n. it needs to at least be 301 n for the box to move because then it is an unbalanced force and it will move the way that the greater force is pushing it. if you use only 300 n it will be a balanced force and will not move because the force you are exerting on the   box is the same as its force.

hope this !

im sorry if i went too in depth, i am going to include a link to a video on khan academy that will explain this.   hope that you like the video and that it explains more in detail to you.

that is the link.

if the person is shown to have +90n, then ans is -10n.

if the person is shown to have -90n, then ans is +10n.