How does the atmosphere act as a blanket?
The atmosphere acts as a blanket by performing the following functions:
(a) Ozone absorbs harmful UV radiations coming from the Sun.
(b) Carbon-dioxide and water vapours trap the heat and regulate the temperature of the Earth by keeping it ambient by absorbing heat rays during the day and by reflecting the heat trapped during the daytime at night.
(c) It slows down the escape of heat from the surface of the Earth into outer space during night time.
Therefore, the atmosphere covers and protects the Earth like a blanket.
Abdul, while driving to school, computes the average speed for his trip to be 20 km h-1. On his return trip along the same route, there is less traffic and the average speed is 40 km h-1. What is the average speed for Abdul’s trip?
An object of mass 40 kg is raised to a height of 5 m above the ground. What is its potential energy? If the object is allowed to fall, find its kinetic energy when it is half-way down.
A driver of a car travelling at 52 km h-1 applies the brakes and accelerates uniformly in the opposite direction. The car stops in 5 s. Another driver going at 3 km h-1 in another car applies his brakes slowly and stops in 10 s. On the same graph paper, plot the speed versus time graphs for the two cars. Which of the two cars travelled farther after the brakes were applied?
Fig 8.11 shows the distance-time graph of three objects A,B and C. Study the graph and answer the following questions:
Fig. 8.11
(a) Which of the three is travelling the fastest?
(b) Are all three ever at the same point on the road?
(c) How far has C travelled when B passes A?
(d) How far has B travelled by the time it passes C?
Two objects, each of mass 1.5 kg, are moving in the same straight line but in opposite directions. The velocity of each object is 2.5 m s-1 before the collision during which they stick together. What will be the velocity of the combined object after collision?
Soni says that the acceleration in an object could be zero even when several forces are acting on it. Do you agree with her? Why?
Two objects of masses 100 g and 200 g are moving along the same line and direction with velocities of 2 m s-1 and 1 m s-1, respectively. They collide and after the collision, the first object moves at a velocity of 1.67 m s-1. Determine the velocity of the second object.
How do poriferan animals differ from coelenterate animals?
The speed-time graph for a car is shown is Fig. 8.12.
Fig. 8.12
(a) Find how far does the car travel in the first 4 seconds. Shade the area on the graph that represents the distance travelled by the car during the period.
(b) Which part of the graph represents uniform motion of the car?
How are sol, solution and suspension different from each other?
Why is the atmosphere essential for life?
Why is it advised to tie any luggage kept on the roof of a bus with a rope?
Using a horizontal force of 200 N, we intend to move a wooden cabinet across a floor at a constant velocity. What is the friction force that will be exerted on the cabinet?
How are the wavelength and frequency of a sound wave related to its speed?
What are the advantages of inter-cropping and crop rotation?
What are the functions of the stomata?
Diagrammatically show the difference between the three types of muscle fibres.
Name A,B,C,D,E and F in the following diagram showing change in its state
What is the role of epidermis in plants?
Where is apical meristem found?