Q

2. Fill in the blanks:

(v) Motion of wheel of a bicycle is______________.

P Plabita

Motion of wheel of a bicycle is circular.

2. Fill in the blanks:

(iv)Motion of the needle of a sewing machine is ______________.

P Plabita

Motion of the needle of a sewing machine is periodic.

2. Fill in the blanks:

(iii)Motion of a child on a swing is ______________.

P Plabita

Motion of a child on a swing is periodic.

2. Fill in the blanks:

(ii) Five kilometre is ______________ m.

D Divya Prakash Singh

Five kilometre is 5000 m.

$\\1 km = 1000 m\\ 5 km = 5 \times 1 km\\ 5 km = 5 \times 1000 m\\ 5 km = 5000 m$

2. Fill in the blanks: (i) One metre is ______________ cm

D Divya Prakash Singh

One metre is 100 cm.

1. Give two examples each, of modes of transport used on land, water and air.

D Divya Prakash Singh

Two examples of modes of transport used on land are cars and bicycles.

Two examples of modes of transport used on water are submarines and ships.

Two examples of modes of transport used in air are aeroplanes and helicopters.

7. A bag of cement lying in the open gets wet due to rain during the night. The next day the sun shines brightly. Do you think the changes, which have occurred in the cement, could be reversed?

D Divya Prakash Singh

Once cement mixes with water they both react together and the substance formed hardens and this change cannot be reversed.

6. A thick coating of a paste of Plaster of Paris (POP) is applied over the bandage on a fractured bone. It becomes hard on drying to keep the fractured bone immobilised. Can the change in POP be reversed?

D Divya Prakash Singh

On mixing POP with water the POP reacts with water to give a differenet substance and this change cannot be reversed.

5. Give examples to explain the difference between changes that can or cannot be reversed.

D Divya Prakash Singh

The following examples explain the differences between changes that can or cannot be reversed.

(a). A ball of clay shaped into a pot can be brought back to its original shape and therefore the change can be reversed. However if it is baked the pot thus formed cannot be changed back to soft clay and therefore the change cannot be reversed.

(b). Pieces of raw vegetables mixed together can be seperated and therefore the change(the mixing) can be reversed but if we cook the vegetables they cannot be brought back to the raw state and therefore the change cannot be reversed.

4. A drawing sheet changes when you draw a picture on it. Can you reverse this change?

D Divya Prakash Singh

The answer depends on using what kind of material the drawing has been made. If it has been made using a pencil then the drawing might be erasable and the change can be reversed but if the drawing has been made using a pen or marker then the drawing is permanent and it cannot be erased and hence the change cannot be reversed.

3. Some changes are listed in the following table. For each change, write in the blank column, whether the change can be reversed or not.

 S. No. Change Can be reversed (Yes/No) 1. The sawing of a piece of wood. 2. The melting of ice candy. 3. Dissolving sugar in water. 4. The cooking of food. 5. The ripening of a mango. 6. Souring of milk.

D Divya Prakash Singh
 S. No. Change Can be reversed (Yes/No) 1. The sawing of a piece of wood. No. 2. The melting of ice candy. Yes. 3. Dissolving sugar in water. Yes. 4. The cooking of food. No. 5. The ripening of a mango. No. 6. Souring of milk. No.

2. You accidentally dropped your favourite toy and broke it. This is a change you did not want. Can this change be reversed?

D Divya Prakash Singh

No. This change cannot be reversed.

1. To walk through a waterlogged area, you usually shorten the length of your dress by folding it. Can this change be reversed?

D Divya Prakash Singh

Yes this change can be reversed.

5. Fill in the blanks.

(d) Night blindness is caused due to deficiency of ____________ in our food.

D Divya Prakash Singh

Vitamin A

5. Fill in the blanks.

(c) Deficiency of Vitamin C causes a disease known as ______________.