or, a = (vu)/t
or, = [20 ms^{1} 0 ms^{1}] / 300
or, a = 1/15 ms^{2 }
(ii) Using third equation of motion,
v^{2} –u^{2} = 2as
or, s = (v^{2} –u^{2})/2a
= [(20 ms^{1})^{ 2} (0 ms^{1})^{ 2}] / 2 x (1/15) ms^{2}
= 3000 m
= 3 km
The acceleration of the train is 1/15 ms^{2} & the distance traveled is 3 km.
(a) What will be the formula of its chloride ?
(b) What will be the formula of its sulphide ?
(c) What will be the formula of its bromide?
Valency of S = 2
Valency of Br = 1
(a) Formula of chloride of element X
Symbols X Cl
Valencies 4 1
The formula of chloride of element X = XCl_{4}
(b) Formula of sulphide of element X
Symbols X S
Valencies 4 2
The formula of sulphide of element X = XS_{2}
(c) Formula of sulphide of element X
Valencies 4 1
The formula of chloride of element X = XBr_{4}
A sample of an element Z contains two isotopes Z35 and Z37. If the average atomic mass of this sample is 35.5u, calculate the percentage of the two isotopes in this sample.
The mass of Z35 is 35 u. Let its percentage in the sample is x%
The mass of Z37 is 37 u. its percentage in the sample be (100x) %
Therefore,
Thus, Z35 = 75%
Z37 = (10075)% = 25%
(A) A gas fills completely the vessel in which it is kept.
(B) A gas exerts pressure on the walls of the container.
(C) A wooden table should be called a solid.
(B) The particles in all the gases move with high speeds in all directions. When these particles strike the walls of the container, they exert force on the walls of the container. Force per unit area is called pressure. So, gases exert pressure on the walls of the container due to the impact of the striking particles.
(C) Because
1. It has a fixed shape and definite volume.
2. It is rigid and cannot be deformed easily as the intermolecular forces in wood are strong.
a) Name the given cell organelle.
b) State any of its two important functions.
a) Golgi Apparatusb) Two important functions are:
i) Packages and dispatches the material synthesised in the cell.
ii) Produces vacuoles or secretory vesicles that contain cellular secretion.
Now, the mass of the ball = 150g = (150/1000)kg
A truck and a car, both moving with a velocity of magnitude v, have a head on collision and both of them come to halt after collision. If the collision lasts for 1s:
(i) Which one of the two vehicle experiences the greater force of impact?
(ii) Which vehicle experiences the greater change in momentum?
(iii) Which vehicle experiences the greater acceleration?
(i) The car will experience the greater force of impact exerted by the truck because truck has greater momentum.
(ii) Change in momentum = Initial momentum – final momentum = m (u  v). As the mass of truck is greater than the mass of the car, so the truck will experience the greater change in momentum.
(iii) The car will experience a greater acceleration after collision.
The stone is being dropped freely from rest, so the initial velocity of the stone, u = 0.Again, the velocity of the stone is increasing as it comes down, so the acceleration due to gravity ‘g’ is to be taken as positive.
Here, Initial velocity u = 0 m/s
Time taken t = 2.0 s
Let h be the height of the bridge
Apply, 2nd kinematic equation;
h = ut + (1/2)gt^{2}
Or, =[0 + (1/2)9.8(2.0)^{2}]m
Or, = 19.6 m
An object of mass 40 kg is placed at point A, which is at a height of 50 m from the ground. If 75% of the gravitational potential energy at point A becomes kinetic energy when the object reaches point B, which is at a height of 30 m, then calculate its speed at point B.
Mass of the body, m = 40 kg; height of point A,
h = 50 m;
gravitational potential energy, E_{p} = mgh
= (40 × 10 × 50) J
= 2 × 10^{4} J or 20 kJ
According to the question,
Kinetic energy at B, E_{k} = 75% of Ep
(a)Write the electronic configuration of the following elements:
(b) Atom is electrically neutral. Why?
(c) Identify a pair of isotopes and isobars from the following:
(b) The beads provide larger surface for the vapours to cool and condense repeatedly and quickly.
(c) Crystallisation is a better technique to separate sugar from sugar solution as compared to evaporation because sugar will char on prolonged and strong heating. The sugar obtained by this technique will be more pure as it will be free from soluble impurities.
1. Speed
2. Average speed
3. Velocity
4. Average Velocity
5. Acceleration.Speed= d / t
S.I. unit of speed = meter/sec =m/s or ms^{1 }
2.Average speed = Total Distance travelled / Total time taken
v_{av} or v = D / T
S.I. unit of average speed = m/s or ms^{1 }
3.Velocity, V = Displacement (d) / Time interval (t)
or, V = d / t
S.I. unit of velocity= m/s or ms^{1 }
4.Average velocity = (initial velocity + final velocity) / 2
V_{av} = (u + v ) / 2
Here; u = initial velocity, v = final velocity.
S.I. unit of V_{av} = m/s
5. Acceleration= change in velocity/ time taken
Change in velocity= final velocity  initial velocity
Acceleration of the body (a) = (v  u) / t
S.I. unit= m/s^{2 }or ms^{2 }
^{ }^{ }
What happens to the force between two objects, if(i) Mass of one object is tripled?
(ii) Distance between the objects is doubled?
(iii) Masses of both objects are doubled?
The force between two objects is given by ‘Universal gravitation law’. It is stated as,
F = G (m_{1}m_{2})/d^{2}
(i) Mass of one object is tripled:
F = (3m_{1})m_{2}/d^{2}
F = 3 G (m_{1}m_{2})/d^{2}
Force will be tripled.
(ii) Distance between the objects is doubled:
F = G (m_{1}m_{2})/(2d)^{2}
F = G (m_{1}m_{2})/4d^{2}
F = 1/4 {G (m_{1}m_{2})}/d^{2}
Force will reduce to onefourth of its previous value.
(iii) Masses of both objects are doubled:
F = G{(2m_{1})(2m_{2})}/d^{2}
F = G{(2m_{1})(2m_{2})}/d^{2}
F = 4 G{m_{1}m_{2}}/d^{2}
Force will be four times greater than its previous value.
It is the number of oscillations produced in one second.
No. of waves produced in 5 seconds = 2,500
So, the no. of waves produced in 1 second = 2,500/5= 500.
Under which of the given situations, a student is most likely to fall sick when:
• He is taking an examination.
• He travels continuously for two days.
• His friend is suffering from measles.
Give reasons in support of your answer.
Student is most likely to fall sick when his friend is suffering from measles. Measles is an infectious disease and the student may contract it from his freind.
Organism  Desired Characters 
 Pest resistance 
Layers 

 Long lactation period 
Fish 

Organism  Desired Characters 
Crops  Pest resistance 
Layers  Egg production 
Cow  Long lactation period 
Fish  High protein content 
Name the types of waves, which are produced when a slinky is plucked as shown in the given cases. Give reason for your answer.
Figure (a) shows the transverse waves while figure (b) shows the longitudinal waves.
Reason:
In case (a), each individual coil of the slinky moves in a direction perpendicular to that of the propagation of waves. So, it is a transverse wave.
In the case (b), compressions and rarefactions travel in a direction parallel to that of the propagation of waves. So, it is a longitudinal wave.
Two spring balance are attached to each other as given in the figure:
If some force pulls the right spring balance will the left spring balance show the same reading? Why?
The left spring balance will show the same reading because to every action, there is equal and opposite reaction. If the right spring balance is pulled, it will exert an equal and opposite force on the left spring.
Take your CBSE board preparation to another level with AI based and rich media animation on Extramarks  The Learning App.
Features of Learning App