Question:
Write the standard equations of motion when an object is thrown upwards with some initial velocity?
Answer:
When an object is thrown upwards with initial velocity (u), it reaches to certain height(h) and its velocity (v) becomes zero. Then it starts to fall. In this case, the acceleration due to gravity (g) is opposing the vertical upward motion and is taken as negative(-ve).
Equations become:
v = u + at ⇒ 0 = u - gt ⇒ u = gt
S = ut + ½at2 ⇒ h = ut - ½gt2
v2 - u2 =2aS ⇒ 0 - u2 =-2gh ⇒ u2 = 2gh
Gravitation
Q 1.
State Kepler’s Laws of planetary motion. How did Newton guess inverse square law ?
Q 2.
What do we call the gravitational force between the Earth and an object ?
Q 3.
Calculate the force of gravitation between the Earth and the Sun,given that the mass of the Earth =
kg and mass of the Sun =
kg. The average distance between the two is
m.
Q 4.
Is weight a scalar quantity?
Q 5.
Can you calculate density of Earth from Newton’s law of gravitation ?
Q 6.
In Fig.,the line that joins a planet to the sun sweeps out areas
,
in time intervals 6 weeks,3 weeks and 2 weeks respectively.How are
,
realted ?
Q 7.
What is the value of ‘g’ at the centre of Earth ?
Q 8.
Why do sewing needles and all pins have a sharp pointed tip?
Q 9.
Fill in the blanks :
Weight of an object is the product of ______ and ________.
Q 10.
What do you mean by acceleration due to gravity ?
Q 11.
The distance between two objects is doubled. What happens to gravitational force between them
Q 12.
At what height above the surface of the earth, the value of 'g' becomes 64% of its value at the surface of the earth. Take radius of the earth = 6400 km.
Q 13.
Two stones A and B are dropped from a multistoried building. A is dropped from 100 m and after some time B is dropped from 50 m height. Both of them reach the earth at the same time. Will they have equal velocity while reaching the ground ? Calculate and find out the answer (take g =10 m/s
2).
Q 14.
Calculate the value of acceleration due to gravity on Moon. Given mass of Moon =
kg, radius of Moon = 1740 km
Q 15.
Suppose a planet exists whose mass and radius both,are half those of Earth.Calculate the acceleration due to gravity on the surface of this planet.
Q 16.
What is the gravitational force between the Earth and a body called? In which direction does it occur?
Q 17.
Fill in the blanks :
Every object in the universe ________ other bodies.
Q 18.
You find your mass to be 42 kg on a weighing machine. Is your mass more or less than 42 kg?
Q 19.
What is the gravitational acceleration of a spaceship at a distance equal to two Earth’s radius from the centre of the Earth ?
Q 20.
Can a body have weight but no mass ?
Q 21.
Fill in the blanks :
Geocentric model i.e. the Earth is the orbital centre of all celestial bodies was proposed by _____.
Q 22.
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.
Q 23.
(a) What is the relationship between g and G?
(b) Show mathematically whether g (acceleration due to gravity on the earth) depends on the mass of the object itself or not.
(c) Show that for a given location on the surface of the earth g is almost constant.
Q 24.
Name the scientist who identified the relation about force of gravitation. Name the law.
Q 25.
Fill in the blanks :
The gravitational force between the earth and the object is generally called ____________.
Q 26.
Why is it difficult to hold a school bag having a strap made of a thin and strong string?
Q 27.
A boy on a clif£ 49 m high drops a stone.One second later,he throws a second stone after the first.They both hit the ground at the same time. With what speed did he throw the second stone ?
Q 28.
A particle is dropped from a tower 180 m high.How long does it take to reach the ground ? What is the velocity when it touches the ground ? Take g =
Q 29.
What is the acceleration of free fall ?
Q 30.
Then why Is the Earth not seen moving towards the stone ?
Q 31.
What are the Kepler Laws that govern the motion of the planets?
Q 32.
Who measured the value of G first time, experimentally?
Q 33.
What happens to 'g' experienced by a body when it moves up the earth's surface?
Q 34.
Gravitational force acts on all objects in proportion to their masses. Why then, a heavy object does not fall faster than a light object?
Q 35.
Define weight? How it is related to mass?
Q 36.
Mass of an object is 10 kg. What is its weight on the Earth? (g = 9.8 m/s
2.)
Q 37.
Write the standard equations of motion when an object is thrown upwards with some initial velocity?
Q 38.
Fill in the blanks :
The acceleration which causes changes only in direction of the velocity of a body is called __________ and it is always directed ___________ the circle.
Q 39.
Fill in the blanks :
A body is said to be in _______ when only gravity acts on it.
Q 40.
Fill in the blanks :
The SI unit of mass is ______.
Q 41.
The pressure at the bottom of a filled glass (density = 1000 kg/m
3) of water is P. The water is taken out and the glass is filled with kerosene oil (density = 817.5 kg/m
3). Now the pressure at the bottom will be a. same as P b. smaller than P c. larger than P d. cannot be determined.
Q 42.
Why will a sheet of paper fall slower than one that is crumpled into a ball?
Q 43.
In what direction does the buoyant force on an object immersed in a liquid act?
Q 44.
The volume of 50 g of a substance is 20 cm
3. If the density of water is 1 g cm
-3, will the substance float or sink?
Q 45.
As you climb up a mountain, your ears “pop” because of the changes in atmospheric pressure. In which direction, outward or inward, does your eardrum move when you climb up?
Q 46.
Relative density of silver is 10.8. If the density of water is 10
3kg/m
3, find density of silver.
Q 47.
What do you mean by free fall ?
Q 48.
A stone is thrown vertically upward with an initial velocity of 40 m/s.Taking g =
,find the maximum height reached by the stone.What is the net displacement and the total distance covered by the stone ?
Q 49.
Which force revolves Moon around Earth ?
Q 50.
Which force accelerates a body in free fall ?
