Laws Of Motion

Step 1: Understanding the Question:
The question asks for the Velocity Ratio (VR) of a block and tackle system that has a total of two pulleys.
Step 2: Key Formula or Approach:
In an ideal block and tackle system, the Velocity Ratio (VR) is defined as the ratio of the distance moved by the effort ( ) to the distance moved by the load ( ).
For a block and tackle system, the VR is equal to the total number of pulleys in the system, which is also equal to the number of rope segments supporting the load.
where is the total number of pulleys.
Step 3: Detailed Explanation:
The problem states that the block and tackle system has a total of two pulleys ( ).
In a typical setup with two pulleys, there would be one fixed pulley in the upper block and one movable pulley in the lower block. The load is supported by two segments of the rope.
When the effort end of the rope is pulled by a distance , each of the two supporting rope segments shortens by . Therefore, the load moves up by a distance , and .
Using the formula for VR:
Alternatively, using the direct relationship for a block and tackle system:
The phrase "effort in the upward direction" describes a specific arrangement, but in a standard block and tackle, the VR depends only on the number of pulleys.
Step 4: Final Answer:
Given that there are two pulleys in the system, the Velocity Ratio is 2.

Step 1: Understanding the Question:
The question asks for the condition required for a body to be in dynamic equilibrium.
Step 2: Detailed Explanation:
Equilibrium refers to a state where the net force acting on a body is zero.
There are two types of equilibrium:
1. Static Equilibrium: The body is at rest (velocity is zero).
2. Dynamic Equilibrium: The body is moving with a constant velocity.
According to Newton's Second Law of Motion, the net force acting on a body is equal to the product of its mass (m) and acceleration (a), i.e., .
For any type of equilibrium, the net force must be zero ( ).
Therefore, . Since the mass (m) of the body is non-zero, its acceleration (a) must be zero.
Let's analyze the given options:
(A) Momentum should be zero: Momentum ( ). In dynamic equilibrium, velocity (v) is constant but not zero, so momentum is also constant but not zero. This is incorrect.
(B) Acceleration should be zero: If acceleration is zero, the velocity is constant. This is the definition of dynamic equilibrium. This is correct.
(C) Kinetic energy should be zero: Kinetic energy ( ). In dynamic equilibrium, velocity (v) is non-zero, so kinetic energy is also non-zero. This is incorrect.
(D) Velocity should be zero: Zero velocity corresponds to static equilibrium, not dynamic equilibrium. This is incorrect.
Step 3: Final Answer:
The condition for a body to be in dynamic equilibrium is that its acceleration must be zero, which means it moves at a constant velocity.