Question

Three blocks with masses m, 2m and 3m are connected by strings, as shown in the figure. After an upward force F is applied on block m, the masses move upward at constant speed v. What is the net force on the block of mass 2 m? (g is the acceleration due to gravity)

• A. Zero
• B. 2 mg
• C. 3 mg
• D. 6 mg

Answer 1

The Correct Option is A

To understand the problem, let's analyze the scenario: We have three blocks with masses \( m \), \( 2m \), and \( 3m \) connected by strings and an upward force \( F \) is applied on the block with mass \( m \). These blocks are moving upward at a constant speed \( v \). We are required to find the net force on the block of mass \( 2m \).

Key points to consider:

1. When an object is moving at a constant speed, its acceleration is zero.
2. According to Newton's second law of motion, the net force \( F_{\text{net}} \) acting on an object is given by: F_{\text{net}} = m \cdot a, where \( m \) is the mass and \( a \) is the acceleration.
3. Since the acceleration \( a = 0 \) (constant speed), the net force must also be zero.

Thus, since the block with mass \( 2m \) is moving at constant speed, the net force acting on it is:

F_{\text{net}} = 2m \cdot 0 = 0

Therefore, the net force on the block of mass \( 2m \) is indeed Zero.