Page No - 55
What name is given to the product of mass and velocity of a body ?
The product of mass and velocity of a body is called momentum.
Name the physical quantity which is considered to be a measure of the quantity of motion of a body.
Momentum is the measure of quantity of motion of a body
What is the SI unit of momentum ?
The SI unit of momentum is kilogram meters per second(kg.m/s)
State whether momentum is scalar or vector.
Momentum is a vector quantity and is dirceted along the direction of velocity.
What is the total momentum of the bullet and the gun before firing ?
The total momentum of the bullet and the gun before firing would be zero because velocities of both of them will be zero.
Name the physical quantity whose unit is kg.m/s.
Momentum has its SI unit as kilogram meters per second(kg.m/s)
What will be the momentum of a body of mass ‘m’ which is moving with a velocity V ?
Momentum of a body of mass ‘m’ and velocity ‘v’ will be
p = m x v
What is the usual name of the forces which cannot produce motion in a body but only change its shape ?
Balanced forces cannot produce motion in a body but can its shape.
Name the unbalanced force which slows down a moving bicycle when we stop pedalling it.
Frictional force slows down a moving bicycle when we stop pedaling it.
State whether the following statement is true or false :
Unbalanced forces acting on a body change its shape.
The given statement is false.
When a ball is dropped from a height, its speed increases gradually. Name the force which causes this change in speed.
Force of gravity causes this change in speed.
Name the property of bodies (or objects) to resist a change in their state of rest or of motion.
Inertia is the property of bodies to resist a change in their state of rest or motion
What is the other name of Newton’s first law of motion ?
Newton’s first law of motion is also known as Galileo’s law of inertia.
The mass of object A is 6 kg whereas that of another object B is 34 kg. Which of the two objects, A or B, has more inertia ?
Object B has more inertia. Since mass is a measure of inertia of a body and object B has greater mass, so it will have greater inertia.
Name the scientist who gave the laws of motion.
Isaac Newton gave the laws of motion.
State whether force is a scalar or a vector quantity.
Force is a vector quantity.
With which physical quantity should the speed of a running bull be multiplied so as to obtain its momentum ?
The speed of the running bull should be multiplied with its mass to get its momentum.
Fill in the following blanks with suitable words :
(a) ………………is a measure of the inertia of a body.
(b) When a running car stops suddenly, the passengers are jerked …………………..
(c) When a stationary car starts suddenly, the passengers are jerked …………………..
(d) Newton’s first law of motion is also called Galileo’s law of ………………………
(e) If there were no unbalanced force of……………….. and no…………………. resistance, a moving bicycle would go on moving for ever.
e) friction; air
Explain why, it is easier to stop a tennis ball than a cricket ball moving with the same speed.
Since the speed of tennis ball and cricket ball is same, the momentum of cricket ball will be higher due to its mass being greater than mass of tennis ball. So, less force is required to stop a tennis ball than to stop a cricket ball.
Explain the meaning of the following equation : .
p = m x v
where symbols have their usual meanings.
p = m x v
This equation signifies that momentum of a body is the product of its mass and its velocity.
Here, p is momentum of the body
m is the mass of the body
v is the velocity of the body.
Explain how, a karate player can break a pile of tiles with a single blow of his hand.
A karate player can break a pile of tiles with a single blow because he strikes the pile with his hand very fast. In doing so, the large momentum of his hand is reduced to zero in a very short time. This exerts a large force on the pile of tiles which is sufficient to break them apart.
Calculate the momentum of a toy car of mass 200 g moving with a speed of 5 m/s.
Mass of the toy car,
m = 200 g = 0.2 kg
Speed, v = 5 m/s
Momentum, p = m x v
= 0.2 x 5 = 1 kg.m/s
What is the change in momentum of a car weighing 1500 kg when its speed increases from 36 km/h to 72 km/h uniformly ?
Mass of car = 1500 kg
Velocity v1 = 36 km/hr = 10 m/s
Momentum p1 = 1500 x 10 = 15000 kg.m/s
Velocity v2 = 72 km/hr = 20 m/s
Momentum p2 = 1500 x 20 = 30000 kg.m/s
Change in momentum = p2-p1= 30000 – 15000 = 15000 kg.m/s
A body of mass 25 kg has a momentum of 125 kg.m/s. Calculate the velocity of the body.
Mass of the body, m = 25 kg
Momentum p = 125 kg.m/s
p = m x v
Calculate the momentum of the following :
(a) an elephant of mass 2000 kg moving at 5 m/s
(b) a bullet of mass 0.02 kg moving at 400 m/s
a) Mass of elephant = 2000kg
Velocity = 5 m/s
Momentum = 2000 x 5 = 10000 kg.m/s
b) Mass of bullet = 0.02 kg
Velocity = 400 m/s
Momentum = 0.02 x 400 = 8 kg.m/s
|1. What is the force and law of motion?|
|2. What are the three laws of motion?|
|3. Can you give an example of the first law of motion?|
|4. How is force calculated according to Newton's second law of motion?|
|5. What is the significance of Newton's third law of motion?|