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# Tag Archives: Newton

## Physics Video Project

The video project was given in 2008 for XI class students of Meghalaya. The best video among them is posted here. Though there are some errors, the video is inspiring to note the work done entirely from scratch by the XI Class students.

## Numericals from Newton’s Laws of motion based on F=ma (For calss XI students of Kendriya Vidyalaya Pattom)

Download the questions and solve them and submit on or before 9 Oct 2014

- A force acts for 10 s on a body of mass 10 kg after which the force ceases and the body describes 50 m in the next 5 s. Find the magnitude of the force. [Ans: 10 N]
- A truck starts from rest and rolls down a hill with constant acceleration. It travels a distance od 400 m in 20s. Calculate the acceleration and the force acting on it if its mass is 7 metric tonnes. [Ans: 2 m/s
^{2}, 14000N] - A motor car running aat the rate of 7 m/s can be stopped by applying brakes in 10 m. Show that total resistance to the motion, when the brakes are on is one fourth of the weight of the car.
- In an Xray machine, an electron is subjected top a force of 10
^{-23}N. In how much time the electron will cover a distance of 0.1 m,? Take the mass of the electron = 10^{-30}kg

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## Numericals from Newton’s Laws of motion based on F=ma (For calss XI students of Kendriya Vidyalaya Pattom)

Download the questions and solve them and submit on or before 9 Oct 2014

- A force acts for 10 s on a body of mass 10 kg after which the force ceases and the body describes 50 m in the next 5 s. Find the magnitude of the force. [Ans: 10 N]
- A truck starts from rest and rolls down a hill with constant acceleration. It travels a distance od 400 m in 20s. Calculate the acceleration and the force acting on it if its mass is 7 metric tonnes. [Ans: 2 m/s
^{2}, 14000N] - A motor car running aat the rate of 7 m/s can be stopped by applying brakes in 10 m. Show that total resistance to the motion, when the brakes are on is one fourth of the weight of the car.
- In an Xray machine, an electron is subjected top a force of 10
^{-23}N. In how much time the electron will cover a distance of 0.1 m,? Take the mass of the electron = 10-30 kg

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## Gravity and Galileo

How Galileo gave acceleration due to gravity before Newton discovered gravity . exactly what happen

Asked Nikhil

Answer:

Newton stated the Universal Law of gravitation and explained why objects fall to earth when dropped.

But objects were falling even before Newton explained it.

The concept of speed and velocity was known before the Law of Gravitation was formulated.

## Does Newton’s Third Law apply on throwing butter on a wall?

Newton’s third law of motion states that

“When we throw any object on anything, that thing also pushes back with the same force. But when we throw butter on the wall, it sticks on the wall. Why?”

Asked by Akshit and Koushal from Class VII A from Kendriya Vidyalaya Air Force Station Bidar, Karnataka

**Answer**:

I feel that there is some misconception/misunderstanding here.

Newton’s Third law states that whenever two bodies interact each other, the force exerted by one body on the other is equal and opposite to the force exerted by the second body on first. These forces are simultaneous and are exerted on different bodies. tha is; the force exerted by the first body is acting on the second body and the force exerted by the second body is acted on the first body.

It doesn’t matter whether the body sticks to the other body or bounces back. We are concerned here with force and not with the motion.

When handful of butter (or clay) is thrown on to the wall, the ball of butter exerts some force on the wall. The wall exerts an equal force simultaneously. But the adhesive force between the wall and butter is more than the force acting on butter which tries to detach it. So it is not detached.

When a rubber ball thrown on the wall, the force exerted by the wall on the ball compresses it. Due to the elastic nature of the ball, it tries to bring the shape back to original and this makes it bounce back. The force exerted on the wall due to the bouncing ball is double that of a clay/butter ball of same mass hitting the the wall with same speed; because, the rubber ball requires the force to bounce back too.

Also refer to http://hyperphysics.phy-astr.gsu.edu/hbase/truckc.html#c1

http://www.phy-astr.gsu.edu/dhamala/Physics2211/Chapter9.pdf

## Body at incline

1. In first case we have the box with weight, say, 10 Newtons on incline. We calculate two components (perpendicular and parallel)of weight. We calculate normal force and force of friction. The box is at rest.

2. In second case we have ball on incline, made of same material as box from first case. Weight of the ball is the same as in first case, components of weight are the same as in first case. Normal force and friction have the same amount as in the case of box. But,unlike the box, ball is moving – it slides down. How’s that possible? If calculated net force is zero?

** Petar asked**

Answer:

It is not true that the **ball slides, ** but it will roll down.

In the first case, the forces balance each other and there is no motion.

In the second force, the frictional force acting tangentially backwards (up the incline) and the component of weight of the ball acting parallel to the plane and through the centre of the ball constitute a couple and tends to rotate it. Now there is no sliding; it rolls.

*(If any further clarification is required please post as comment to this post)*

Please refer to http://www.real-world-physics-problems.com/rolling-without-slipping.html for detailed treatment of the Physics of rolling without friction.

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## Newton’s Third Law of Motion and some doubts

Newton’s Third Law of Motion states that

“Every action has equal and opposite reaction”

In other words,

“Whenever a body exerts a force on another body, the second body exerts an equal and opposite force on the first body”

Osho Garg asks:

“if a person is sitting on a chair both the chair and person exert force against it so we called that ” there is always an equal and opposite reaction ” but for example a elephant of mass 584 kg sit on a chair, the chair will broke. So what we called for this . Please explain.

Answer:

When an elephant “sits” on a chair, it breaks because it cannot give the “equal reaction” and it “yields” to it.

Therefore, here the force is doing “work”.

**More discussions are welcome**

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