Basic Science - Class 7 General Knowledge - Extra Questions

Consider the situation shown in figure. All the surfaces are frictionless and the string and the pulley are light. Find the magnitude of the acceleration of the two blocks.
1889429_dd1eea8e761c45c6816099adb1b14d36.png



Force $$F$$ and density $$d$$ are related as $$F=\frac{\alpha}{\beta+\sqrt{d}}$$ then find the diamention of $$\alpha$$ and $$\beta$$



$$Mass M = 1$$ unit is divided into two parts $$X$$ and $$( 1 - x)$$. For a given separation the value of $$X$$ for which the gravitational force between them becomes maximum is 



A cube of mass $$2\ kg$$ is held stationary against a rough wall by a force $$F = 40\ N$$ passing through centre $$C$$. Find perpendicular distance of normal reaction between wall and cube from point $$C$$. Side of the cube is $$20\ cm$$. Take $$g = 10\ m/s^{2}$$.
1602707_60b12998153a4d11a821f0b81c556047.png



What is a force?



How does the mass of an electron compare to the mass of a proton?



How does one Coulomb of charge compare with the charge of a single electron?



How does static friction differ from kinetic friction?



How does the acceleration of an object depend on the net force acting on it if the total mass is constant?



How does the roughness of surfaces that are touching affect the friction between the surfaces?



A 50 cm long straight piece of thread is kept on the surface of water. Find the force with which the surface on one side of the thread pulls it. Surface tension of water $$-0.076 N/m $$. 



Match column-I with cohimn-II and select the correct answer using the codes given below:



Why does a boatman push the bank with his pole to make the boat move?



Why does a train stop when you pull the chain?



Why does the gun kick back when a bullet is fired?



The acceleration of the $$2\ kg$$ block if the free end of string is pulled with a force of $$20\ N$$ as shown is
1030815_950db6c15ee043dbbfa97d3c5f456632.png



A block is shot with an initial velocity $$5 ms^{-1} $$ on a rough horizontal plane. Find the distance covered by the blocks toll it comes to rest. The coefficient of kinetic friction between the block and plane is $$0.1$$.



What is the acceleration of the body moving with uniform acceleration at the midpoint of two points on a straight line, where the speeds are $$u$$ and $$v$$ respectively?



A rod $$OA$$ of mass $$4\ kg$$ is held in horizontal position by a massless string $$AB$$ as shown in figure. Length of the rod is $$2\ m$$. Find
(a) tension in the string.
(b) net force exerted by hinge on the rod. $$(g = 10\ m/s^{2})$$.
1405222_aeaad29ddbf649728e932735fcd4e1d1.png



Two vectors having magnitude 12 and 13 are inclined at an angle $${45^0}$$ to each other. find their resultant vector.



A force of $$5N$$ acting on a body $$A$$ produces an acceleration of $$2m{s}^{-2}$$. The same force acting on the body $$B$$ produces an acceleration of $$5m{s}^{-2}$$. Find the mass of the bodies $$A$$ and $$B$$. What will be the acceleration produced if both the bodies are tied together and same force (ie $$5N$$) acts on it.



How does the Bohr's model of the atom differ from the quantum mechanical model?



How does oxygen has mass?



What is the mass number of an atom?



A  thin uniform rod of length 1 m and mass 1 kg is roasting an axis passing through its centre and perpendicular to its length . Calculate the moment of inertia and radius of gyration of the rod about an axis passing through a point midway between the centre and its edge, perpendicular to its length . 



A disc with linear velocity $$ v $$ and angular velocity $$ \omega $$ is placed on rough ground. Suppose $$ a $$ and $$ \alpha $$ be the magnitudes of linear and angular acceleration due to friction. Then:
Column IColumn II
(A) When $$ v = R \omega $$ (p) $$ a = R \alpha (a \neq 0) $$
(B) When $$ v = \frac{R \omega}{2} $$(q) $$ a > R \alpha $$
(C) When $$ v = 2 R |omega $$(r)  $$ a > R \alpha $$
(s) None



$$v=at+\cfrac{b}{t+c}$$ is a dimensionally valid equation. Obtain the dimensional formula for $$a,b$$ and $$c$$ where $$v$$ is velocity, $$t$$ is time and $${v}_{0}$$ is initial velocity



A particle describes a horizontal circle of radius  r on a smooth surface of an inverted  cone . The height of the plane of the circle above the vertex is h . Then the speed of the particle will be  



A total charge $$q$$ is distributed uniformly along a thin straight rod of length $$l$$. Choose the positive $$y$$ direction as up and the positive x-direction as up and the positive x direction as right and calculate and express in unit vector notation.
a. the electric field at point $$P_{1} $$ in terms of the given variables
b. the electric field at point $$P_{2} $$ in terms of the given variables
[See integral given on formula page.]
1889389_fd818a64ca3d483abaff32c53acf6bf6.png



A uniform solid cylinder of mass $$M = 2\,kg$$ and radius $$R = 10\,cm$$ is connected about an axis through the centre of the cylinder to a horizontal spring with spring constant $$4\,N/m$$. The cylinder is pulled back, stretching the spring $$1\,m$$ from equilibrium. When released, the cylinder rolls without slipping. What is the speed of the center of the cylinder when it returns to equilibrium?



Find the angle it makes with one of the rectangular components of a force of $$40\,N$$ is $$20\,N.$$ Find the angle it makes with this component.



A heavy ball of mass $$M$$ is suspended from the ceiling of a car by a light string of mass $$m(M<<M)$$. When the car is at rest, the speed of transverse waves in the string is $$60m{s}^{-1}$$. When the car has an acceleration $$a$$, the wave-speed increases to $$60.5m{s}^{-1}$$. The value of $$a$$, in terms of gravitational acceleration $$a$$ is closest to:



Derive the formula for the range and maximum height achieved by a projectile thrown from thee origin with initial velocity u at an angle $$\theta$$ to the horizontal.



In the figure shown masses of the blocks A, B and C are 6 kg , 2Kg and 1 Kg respectively . Masses of the spring is negligibly small and its stiffiness is 100 N/m . The co-efficient of friction between the block A and the table is $$\mu  = 0.8 $$ . Initially block C is held such that spring is i n relaxed position . The block is released from rest Find the maximum distance moved by the block C in cm 



Example 2.12 The periodic of oscillation of a simple pendulum  is T  =  21 . /L /g . Measured value of Lis 20.0 cm known to 1 mm accuracy and time for 100 oscillation  of the pendulum is found to be 90 s using a wrist watch of 1 s resolution  . What is the accuracy in the determination of g ?



A block of wood of mass 0.5 kg is placed on a plane making $$30^{\circ}$$  with the horizontal . If the co-efficient of friction between the surfaces of contact of the body and the plane is 0.5 . What force is required to keep the body sliding down ?



Prove that angle of friction is equal to angle of repose.



In this problem, we will use mechanical similarity to find the period T of simple pendulum ($$\theta$$ is very small).
If gravitational acceleration is changed by a factor $$\alpha$$ and time by a factor $$\beta : g \rightarrow g' = \alpha g, t \rightarrow t' = \beta t,$$ find the relation between $$t' / t$$ and $$g' / g$$
(hint: L' = constant $$\times$$ L)
1889580_075b9c1ec8ed4dc5962fecdb852ea2a7.png



The speed of a motor increases from $$1200 rpm $$to $$1800 rpm$$ in $$205$$. How many revolutions does it make in this period of time?



What do you mean by projectile motion? A point object is projected at an angle $$\theta $$ with the horizontal with velocity u from the ground and the object strikes the ground on the same level as that of projection after some time. Prove that - The trajectory of the projectile is parabolic.



The angular frequency of a fa increases from $$30 rpm$$ to $$60 rpm$$ in $$\pi s$$. A dust particle is present at a distance of $$20 cm$$ from axis of rotation. The tangential acceleration of the particle in $$\pi s$$ is 



Two identical balls of mass $$2 kg$$ each are kept in contact with a compressed spring, on either side of it. When the spring is released, the balls move with a velocity $$10 m s^{-1}$$. Find the acceleration produced in each ball if the spring constant is $$4 N m^{-1}$$



Calculate the height of the communication satellite. $$\left [ Given G = 6.67 \times 10^{-11} Nm^2/kg^2, M = 6 \times 10^{24} kg, R = 6400 km \right ]$$



A ball is thrown from ground such that it just crosses two poles of equal height kept $$ 80 \mathrm{m} $$ apart. The maximum height attained by the ball is $$ 80 \mathrm{m} $$. When the ball passes the first pole, its velocity makes $$ 45^{\circ} $$ with horizontal. The correct alternatives is/are :- $$ \left(g=10 \mathrm{m} / \mathrm{s}^{2}\right) $$
(A) Time interval between the two poles is $$ 4 \mathrm{s} $$(B)Height of the pole is $$ 60 \mathrm{m} $$.
(C) Range of the ball is $$ 160 \mathrm{m} $$.
(D) Angle of projection is $$ \tan ^{-1}(2) $$ with horizontal.



Two balls of equal masses are projected upward simultaneously one from the ground with speed 50 m/s and other from a 40 m high tower initial speed 30 m/s. Find the maximum height attained by their center of mass.



A 4m long ladder weighing 25 kg rests with its upper end against a smooth wall and lower end on rough ground What should be the minimum coefficient of friction between the ground and the ladder for it to be inclined at $$60^{\circ}$$ with the horizontal without slipping ? (Take $$g = 10 ms^{-2}$$)



A  10  kg block kept on an inclined plane is pulled by a string applying 200  N force . A  10 N force is also applied  on 10 kg block as shown in fig Find (a) tension in  the string .
acceleration of 10 kg block
net force on pulley exerted by string .
1899770_191c62ccd1084125bd0f24d6a088643c.PNG



Two forces $$ F_{1} $$ and $$F_{2} (F_{1}- F_{2}) $$ are applied at the free ends of uniform rod kept on a horizontal frictionless surface . The rod has length L and total mass M , Find tension in rod at distance x from end 'A'
1899811_2b87bebbe16e40adb79c1cbfc46b9c60.PNG



In the system shown below , function and mass  of the pulley are neglibible . Find the acceleration of $$ m_{2}$$ if $$ m_{1} =  300 g , m_{2} =  500 g $$ and F  =  1.50 N
1899822_4fe5fea2d4b4445e98db3402e55a5f0d.PNG



A point $$P$$ moves in counter-clockwise direction on a circular path as shown in the figure. The movement of $$P$$ is such that it sweeps out a length $$s= t^3 + 5$$, where $$s$$ is in metre and $$t$$ is in second. The radius of the path is $$29 \ m$$. The acceleration of $$P$$ when $$t= 2s$$ is nearly.
1899851_976d8780340c4cf386bebf1e5e796318.png



A man is running on a hill with velocity (2i+3j)m/s with respect to ground he feels that trained drops are falling vertically with velocity 4m/s. if man is running on heel in a new direction with same speed find velocity of rain with respect to man. 



Find the value of g at a height of 400 km above the surface of the earth. Given radius of the earth, R = 6400 km and value of g at the surface of the earth = $$9.8 ms^{-2}.$$



A particle A moves along a circle of radius R = 50 cm so that its radius vector r relative to the point O (Fig. 1.5) rotates with the constant angular velocity $$\omega = 0.40 rad s^{-1}.$$ Find the modulus of the velocity of the particle, and the modulus and direction of its total acceleration.
1899920_029cf1d353514ddcbf0462dca1773a40.PNG



State Newton's $$ 3^{rd} $$ law of motion. Explain any two examples based on this law.



A $$100\,g$$ ball is coming towards a bat with a velocity of $$10\,m/s.$$ It strikes that bat at $$60^\circ$$ and rebounds. If the ball remains in contact with the bat for $$0.1\,s,$$ what is the force applied on the bat.
1902026_cae3cbeb35c84bbcb06c5ac66327d11e.png



The velocity(v) versus time (t) graph of a body moving on a straight line is shown in figure. The average speed of body in the interval of $$6$$ s is
1902578_1816b3fb729a4412925c5b13c04cf6ff.png



The frictional force acting on $$10\,kg$$ block by the ground is $$\left ( \dfrac{2n + 65}{3} \right )N.$$ Find the value of n.
1902612_b0c8db8524c44396abeede81da1a827b.png



For a particle undergoing rectilinear motion with uniform acceleration, the magnitude displacement is one third the distance covered in some time interval. The magnitude of final velocities is less than the magnitude of initial velocity for this time interval. The ratio of initial speed to final speed for this time interval is $$\dfrac{4\sqrt{2}}{n}$$, Find the value of $$n$$.



A light straight fixed at one end to a wooden clamp on a ground passes over a pulley and hangs at the other side. It makes an angle $$30^o$$ with the ground. A body weighing $$60\ kg$$ climbs up the rope. The wooden clamp and tolerate up to vertical force $$360\ N$$. Find the maximum acceleration in the upward direction with which the boy can climb safely. The friction of pulley and wooden clamp may be ignored $$(g=10\ m/s^2)$$

1903066_4841f36b6dc64a5bb585898fd9de3f1b.png



A wooden plank of mass 20 kg is resting on a smooth horizontal floor. A man of mass 60 kg starts moving from one end of the plank to the other end. The length of the plank is 10 m. Find the displacement of the plank over the floor when the man reaches the other end of the plank,
1903169_baab35df3aa34121aaabf8eca92003c8.png



A bead can freely move on a horizontal rod. The bead is connected by block $$B$$ and $$D$$ by a string as shown in the figure. If the velocity of $$B$$ is $$V$$. Find the velocity of Block $$D$$.
1903378_0bd01a631a7f465aa3a0eefb41dd41b6.png



The force required just to move a body up an inclined plane is double the force required just to prevent the body sliding down it. If the coefficient of friction is $$0.333$$, angle of inclination of the plane is ....



How much force is needed to accelerate a 66 kg skier at $$ 2 m/s^{2}$$



Why action and reaction forces are not balanced forces?



Why $$MgSO_4$$ soluble in water whereas $$BaSO_4$$ is insoluble in water?



What does a skydiver achieve terminal velocity?



Describe any five man-made sources of water?



Two trains start from $$p$$ and $$q$$ respectively and travel towards each other at a speed of $$50\ km/hr$$ and $$40\ km/hr$$ respectively. By the time they meet, the first train has travelled $$100\ km$$ more than the second. The distance between $$p$$ and $$q$$ is:



Examples of static inertia and dynamic inertia



A ball is thrown vertically upwards with a velocity of $$20m/s$$ 
from the top of a multi storey building.The height of the point where the ball is thrown 25 m from the ground.How high will the ball rises.( b) How long it will be before hits the ground.$$g=10m/s^{2}$$



How does the atomic number change when an element emits an alpha particle?



Class 7 General Knowledge Extra Questions