Students of a school staged a rally for cleanliness campaign. They walked through the lanes in two groups. One group walked through the lanes AB, BC and CA; while the other through AC, CD and DA (see Fig. 12.12). Then they cleaned the area enclos

Students of a school staged a rally for cleanliness compaign. They walked through the lanes in two groups. One group walked through the lanes A B , B C a n d C A ; while other through A C , C D a n d D A (See in Figure). Then they cleaned the ara enclosed within their lanes. If A B=9m B C=40 m , C D=15 m , D A=28 m , a n d /_B=90^0dot Which group cleaned more area and by how much? Find the total area cleaned by the students.

Students of a school staged a rally for cleanliness compaign. They walked through the lanes in two groups. One group walked through the lanes A B ,\ B C\ a n d\ C A ; while other through A C ,\ C D\ a n d\ D A (See in Figure). Then they cleaned the area enclosed within their lanes. If A B=9m\ B C=40 m ,\ C D=15 m ,\ D A=28 m ,\ a n d\ /_B=90^0dot Which group cleaned more area and by how much? Find the total area cleaned by the students.

A group of students took an old shoe box and covered it with a black paper from all sides. They fixed a source of light (a torch) at one end of the box by making a hole in it and made another hole on the other side to view the light. They placed a milk sample contained in a beaker/tumbler in the box as shown in the Figure. They were amazed to see that milk taken in the tumbler was illuminated. They tried the same activity by taking a salt solution but found that light simply passed through it ? (a) Explain why the milk sample was illuminated? Name the phenomenon involved. (b) Same results were not observed with a salt solution. Explain. (c) Can you suggest two more solutions which would show the same effect as shown by the milk solution?

For the cuboid shown in figure,the lengths of AB, BC, CG are 12, 8, 6 units respectively. Two points P and Q are chosen such that they are the mid-points of the edges GH and CD respectively. Two cuts are then made using a knife so as to cut the cuboid in to three pieces. The first cut passes through PQ to meet EA. The second cut is made on other side of PQ to meet FB. The difference in the total surface area (in square units) of the biggest of the three new pieces and the total surface area of initial cuboid is :

A closed cubical box is made of perfectly insulating material and the only way for heat to enter or leave the box is through two solid cylindrical metal plugs, each of cross sectional area 12cm^(2) and length 8cm fixed in the opposite walls of the box. The outer surface of one plug is kept at a temperature of 100^(@)C . while the outer surface of the plug is maintained at a temperature of 4^(@)C . The thermal conductivity of the material of the plug is 2.0Wm^(-1)C^(-1) . A source of energy generating 13W is enclosed inside the box. Find the equilibrium temperature of the inner surface of the box assuming that it is the same at all points on the inner surface.

A closed cubical box is made of perfectly insulating material and the only way for heat to enter or leave the box is through two solid cylindrical metal plugs, each of cross sectional area 12cm^(2) and length 8cm fixed in the opposite walls of the box. The outer surface of one plug is kept at a temperature of 100^(@)C . while the outer surface of the plug is maintained at a temperature of 4(@)C . The thermal conductivity of the material of the plug is 2.0Wm^(-1).^(@)C^(-1) . A source of energy generating 13W is enclosed inside the box. Find the equilibrium temperature of the inner surface of the box assuming that it is the same at all points on the inner surface.

There are two towns Ramgarh and Arjangarh which are separated by a hill. The people of one town have to travel on a zig-zag road which goes over the hill so as to reach the other town. Gaurav is a student of class IX in Ramgarh. Onnce Gaurav went from Ramgrah to Arjangarh on a scooter with his father. Driving at a constant speed of 50km/h on the hilly road, it took exactly 30 minute to reach Arjangarh. One day Gaura told his father that if a straight tunnel could be dug through the hill, then it would become very easy for the people of two towns to visit each other. keeping this is mind, Gaurav invited the people of both the towns and took a delegation to the Collector's office. This delegation demanded the construction of a straight tunnel road through the hill. Gaurav explained the various advantages of connecting Ramgarh and Arjangarh through a tunnel road in the hill. The collector liked the idea and a straight tunnel road was constructed after some time. One day Gaurav went from Ramgarh to Arjangarh through the straight tunnel road on the scooter with his father. Driving at a constant speed of 50 km/h, it took them just 12 minutes to reach Arjangarh. Both, Gaurav and his father were very happy. (a) What was the distance covered by Gaurav on going from Ramgarh to Arjangarh by travelling on road over the hill? (b) What is the distance covered by Gaurav on going from Ramgarh to Arjangarh by travelling on straight tunnel road/ (c) How much less distance is to be covered now in going through the tunnel than on going over the hill? (d) What is the displacement of Gaurav from Ramgarh on reaching Arjangarh? (e) State two advantages of construction of the tunnel road for the people of two towns. (f) What values are displayed by Gaurav in this episode?