Question 4

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.

Answer

Mass of one of the objects, m_{1} = 100 g = 100/1000 = 0.1 kg

Mass of the other object, m_{2} = 200 g = 200/1000 = 0.2 kg

Velocity of m_{1} before collision, v_{1} = 2 m/s

Velocity of m_{2} before collision, v_{2} = 1 m/s

Velocity of m_{1} after collision, v_{3} = 1.67 m/s

Velocity of m_{2} after collision = v_{4} = ?

By law of conservation of momentum :

Total momentum before collision = Total momentum after collision

m_{1}v_{1} + m_{2}v_{2} = m_{1}v_{3} + m_{2}v_{4}

(0.1)2 + (0.2)1 = (0.1)1.67 + (0.2)v_{4}

0.4 = 0.167 + 0.2v_{4}

v_{4} = 1.165 m/s

The velocity of the second object after collision 1.165 m/s.

- 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:-
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:-
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? - 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:-
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:-
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:-
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:-
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:-
How are sol, solution and suspension different from each other?

- Q:-
Draw a labelled diagram of a neuron.

- Q:-
Calculate the formula unit masses of ZnO, Na

_{2}O, K_{2}CO_{3}, given atomic masses of Zn=65 u, Na=23 u, K=39 U, C=12 u and O=16 u. - Q:-
With the help of Table 4.1, find out the mass number of oxygen and sulphur atom.

- Q:-
What causes winds?

- Q:-
Define the atomic mass unit.

- 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:-
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:-
Name the tissue responsible for movement in our body.

- Q:-
A certain household has consumed 250 units of energy during a month. How much energy is this in joules?

- Q:-
Calculate the force of gravitation between the earth and the Sun, given that the mass of the earth = 6 × 10

^{24}kg and of the Sun = 2 × 10^{30}kg. The average distance between the two is 1.5 × 10^{11}m.

- NCERT Chapter