Question

Block B is kept on block A which in turn is kept on a horizontal surface. If A is
suddenly accelerated towards right the frictional force on B will be?​

Answer 1

The frictional force on B by A will be in the rightward direction.

Given:

Block B is kept on block A which in turn is kept on a horizontal surface. And then A is accelerated to right.

To Find:

The frictional force on B by A.

Solution:

According to the question, the B block is on top of the A block.

And both of them are on a horizontal surface.

Let, the acceleration of a is made on block A by applying force F, as shown in the figure.

The easiest way to understand the whole body is to understand the free body diagram of each object within it.

So as in the figure free body diagram of blocks A and B is drawn separately.

So, as block A accelerated, it gains a friction force by B, which has been denoted as $F_{ba}$, versed as the frictional force of B on A.

This $F_{ba}$ is directed opposite to the acceleration on A, i.e, on left.

And to oppose this frictional force block B has gained a frictional force  $F_{ab}$ that is the opposite of $F_{ba}$ and is directed towards the right.

Thus, the frictional force on B by A will be in the rightward direction according to Newton's third law.

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Answer 2

A, will exert a rightward-moving frictional force on B.

What is frictional force and examples?

• When the hands are rubbed against each other, a force opposing this motion of the hands comes into action.
• The force resisting the motion is applied in the direction opposite to the direction of motion of the hands is called the frictional force and is responsible to generate heat energy.

How many types of Frictional forces are there?

There are mainly four types of Frictional forces which are given below:

Dry Friction:

• Dry friction explains the reaction between kinetic friction and static friction.
• That is to say, it resists the sliding movement of moving solid on non-moving solid.

Fluid Friction:

• As the name suggests it is the friction of viscous fluid.

Rolling Friction:

• It is the force that opposes the motion of moving rolling solid, such as rolling of the wheels, or ball, or any such solid body.

Sliding Friction:

• This is kinetic friction, and is created when the two rolling bodies slide along with each other.

What is the formula to calculate the frictional force?

• The frictional force is given by the formula: F = μN.

According to the question:

• Block B is kept on block A which in turn is kept on a horizontal surface.
• And then A is accelerated to right.

• According to the question, the B block is on top of the A block.
• And both of them are on a horizontal surface.
• Let, the acceleration of a is made on block A by applying force F, as shown in the figure.
• The easiest way to understand the whole body is to understand the free body diagram of each object within it.
• So as in the figure free body diagram of blocks A and B is drawn separately.
• So, as block A accelerated, it gains a friction force by B, which has been denoted as $F_{ba}$  , versed as the frictional force of B on A.
• This $F_{ba}$ is directed opposite to the acceleration on A, i.e, on left.
• And to oppose this frictional force block B has gained a frictional force $F_{ab}$  that is the opposite of $F_{ba}$ and is directed towards the right.

Hence, A, will exert a rightward-moving frictional force on B.

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