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Laws of Motion question

2025 · 2 Apr · Shift 2 · Q67
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Laws of Motion question

2025 · 2 Apr · Shift 2 · Q67

JEE MainPhysicsLaws of MotionMCQ+4 / −1
JEE Main 2025 (Online) 2nd April Evening Shift Physics - Laws of Motion Question 5 English A body of mass 1 kg is suspended with the help of two strings making angles as shown in figure. Magnitudes of tensions T1\mathrm{T}_1T1​ and T2\mathrm{T}_2T2​, respectively, are (in N ) : (Take acceleration due to gravity 10 m/s210 \mathrm{~m} / \mathrm{s}^210 m/s2 )
  1. A
    53,55 \sqrt{3}, 553​,5
  2. B
    53,535 \sqrt{3}, 5 \sqrt{3}53​,53​
  3. C
    5,5
  4. D
    5,535,5 \sqrt{3}5,53​
View written solutionFree

Correct answer: A

  1. Forces acting on the body

A mass of 1 kg1\,\text{kg}1kg is suspended by two strings. Its weight acts vertically downward:

W=mg=1×10=10 NW = mg = 1 \times 10 = 10\,\text{N}W=mg=1×10=10N

Let the tensions in the two strings be T1T_1T1​ and T2T_2T2​.

From the given standard figure for this question, one string makes 30∘30^\circ30∘ with the horizontal and the other makes 60∘60^\circ60∘ with the horizontal.

  1. Resolve tensions into components

Assume:

  • T1T_1T1​ is in the string making 30∘30^\circ30∘ with the horizontal
  • T2T_2T2​ is in the string making 60∘60^\circ60∘ with the horizontal

For equilibrium:

  • Horizontal components must cancel
  • Vertical components must balance the weight

Horizontal equilibrium

T1cos⁡30∘=T2cos⁡60∘T_1 \cos 30^\circ = T_2 \cos 60^\circT1​cos30∘=T2​cos60∘

T1⋅32=T2⋅12T_1 \cdot \frac{\sqrt{3}}{2} = T_2 \cdot \frac{1}{2}T1​⋅23​​=T2​⋅21​

T2=3 T1T_2 = \sqrt{3}\,T_1T2​=3​T1​

  1. Vertical equilibrium

T1sin⁡30∘+T2sin⁡60∘=10T_1 \sin 30^\circ + T_2 \sin 60^\circ = 10T1​sin30∘+T2​sin60∘=10

Substitute sin⁡30∘=12\sin 30^\circ = \frac{1}{2}sin30∘=21​ and sin⁡60∘=32\sin 60^\circ = \frac{\sqrt{3}}{2}sin60∘=23​​:

T1⋅12+T2⋅32=10T_1 \cdot \frac{1}{2} + T_2 \cdot \frac{\sqrt{3}}{2} = 10T1​⋅21​+T2​⋅23​​=10

Now put T2=3T1T_2 = \sqrt{3}T_1T2​=3​T1​:

T12+32(3T1)=10\frac{T_1}{2} + \frac{\sqrt{3}}{2}(\sqrt{3}T_1) = 102T1​​+23​​(3​T1​)=10

T12+3T12=10\frac{T_1}{2} + \frac{3T_1}{2} = 102T1​​+23T1​​=10

2T1=102T_1 = 102T1​=10

T1=5 NT_1 = 5\,\text{N}T1​=5N

Then,

T2=3×5=53 NT_2 = \sqrt{3} \times 5 = 5\sqrt{3}\,\text{N}T2​=3​×5=53​N

  1. Match with the options

Thus the tensions are:

T1=5 N,T2=53 NT_1 = 5\,\text{N}, \qquad T_2 = 5\sqrt{3}\,\text{N}T1​=5N,T2​=53​N

This corresponds to Option D.

  1. Comparison with stored answer

The stored correct answer is A: 53,55\sqrt{3}, 553​,5.

That would be correct only if the labels T1T_1T1​ and T2T_2T2​ were interchanged in the figure. Based on the usual interpretation described above, the correct ordered pair is:

(T1,T2)=(5,53)(T_1, T_2) = (5, 5\sqrt{3})(T1​,T2​)=(5,53​)

So I disagree with the stored answer unless the figure labels are reversed.

Next

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