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Physics Newton's Laws of Motion Mix Single Correct MCQ
Published on: September 12, 2026

Three masses connected by massless string as shown in figure, are placed on a horizontal frictionless surface. Find tensions T 1 and T 2 .

A
10, 30
B
15, 30
C
20, 30
D
10, 40

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Text Solution

Verified by Experts
The correct answer is:
A
Step 1: Identify the forces acting on the masses in the system. We have three masses:
  • m1 = 10 kg
  • m2 = 20 kg
  • m3 = 30 kg
The total external force acting on the system is 60 N.

Step 2: Calculate the total mass of the system.
Total mass = m1 + m2 + m3
Total mass = 10 kg + 20 kg + 30 kg = 60 kg.

Step 3: Calculate the acceleration of the system using Newton's second law:
F = ma
Therefore, a = \frac{F}{m} = \frac{60 ext{ N}}{60 ext{ kg}} = 1 ext{ m/s}^2.

Step 4: Analyze the forces on each mass to find tensions T1 and T2.
For m3 (30 kg):
\( F_{net} = m_3 imes a \)
\( T_2 = m_3 imes a \)
\( T_2 = 30 ext{ kg} imes 1 ext{ m/s}^2 = 30 ext{ N} \)

For m2 (20 kg):
The tension T1 and T2 acting on m2 gives:
\( T_1 - T_2 = m_2 imes a \)
\( T_1 - 30 = 20 ext{ kg} imes 1 ext{ m/s}^2 \)
\( T_1 - 30 = 20 \)
\( T_1 = 50 ext{ N} \)

For m1 (10 kg):
\( T_1 = m_1 imes a \)
\( T_1 = 10 ext{ kg} imes 1 ext{ m/s}^2 = 10 ext{ N} \)

Therefore, T1 = 10 N and T2 = 30 N.
Therefore, the answer is option A: 10, 30.

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