Question 8

What is the acceleration of free fall?

Answer

When the body falls due to Earth’s gravitational pull, its velocity changes and is said to be accelerated due to Earth’s gravity and it falls freely called free fall. Acceleration of free fall is 9.8 ms^{−2}, which is constant for all objects.

- Q:-
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? - Q:-
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? - Q:-
How do poriferan animals differ from coelenterate animals?

- Q:-
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? - Q:-
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. - Q:-
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?

- Q:-
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? - Q:-
Why are we normally advised to take bland and nourishing food when we are sick?

- Q:-
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.

- Q:-
Why is the weight of an object on the moon 1/6th its weight on the earth?

- Q:-
A ball is thrown vertically upwards with a velocity of 49 m/s. Calculate

(i) the maximum height to which it rises,

(ii) the total time it takes to return to the surface of the earth. - Q:-
A truck starts from rest and rolls down a hill with a constant acceleration. It travels a distance of 400 m in 20 s. Find its acceleration. Find the force acting on it if its mass is 7 metric tonnes (Hint: 1 metric tonne = 1000 kg.)

- Q:-
What happens to the force between two objects, if

(i) the mass of one object is doubled?

(ii) the distance between the objects is doubled and tripled?

(iii) the masses of both objects are doubled? - Q:-
How do poriferan animals differ from coelenterate animals?

- Q:-
A bus decreases its speed from 80 km h

^{-1}to 60 km h^{-1}in 5 s. Find the acceleration of the bus. - Q:-
A freely falling object eventually stops on reaching the ground. What happenes to its kinetic energy?

- Q:-
What precautions can you take in your school to reduce the incidence of infectious diseases?

- Q:-
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? - Q:-
What can you say about the motion of an object whose distance-time graph is a straight line parallel to the time axis?

- Q:-
How does the cork act as a protective tissue?

- NCERT Chapter

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