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Concepts Of Physics MCQ Edition [Volume 1]
Exam
Concepts Of Physics MCQ Edition [Volume 1]
Subject
Physics
Chapter
Newton's Laws of Motion

Concepts Of Physics MCQ Edition [Volume 1] · Physics · Newton's Laws of Motion

Consider the setup presented in the figure. All surfaces are...

Consider the setup presented in the figure. All surfaces are frictionless, while the string and pulley are light. Determine the magnitude of the acceleration of the two blocks.
Consider the setup presented in the figure. All surfaces are frictionless, while the string and pulley are light.

Options

  1. Ag/10g/10
  2. Bg/20g/20
  3. Cg/5g/5
  4. D7g/107g/10

Correct answer

A. g/10g/10

Step-by-step solution

The given wedge forms a triangle with sides 3 m3\text{ m}, 4 m4\text{ m}, and 5 m5\text{ m}. Since 32+42=523^2 + 4^2 = 5^2, it is a right-angled triangle with the right angle at the top vertex.

Let θ1\theta_1 be the angle of inclination of the left surface (length 3 m3\text{ m})andθ2and \theta_2 be the angle of inclination of the right surface (length 4 m4\text{ m}).

Using the geometric properties of the triangle, the altitude hh to the base is given by equating the area:

12×3×4=12×5×h⇒h=125 m\dfrac{1}{2} \times 3 \times 4 = \dfrac{1}{2} \times 5 \times h \Rightarrow h = \dfrac{12}{5}\text{ m}

The sine of the angles of inclination are:

sin⁡θ1=h3=12/53=45\sin \theta_1 = \dfrac{h}{3} = \dfrac{12/5}{3} = \dfrac{4}{5}

sin⁡θ2=h4=12/54=35\sin \theta_2 = \dfrac{h}{4} = \dfrac{12/5}{4} = \dfrac{3}{5}

Let aa be the common acceleration of the two blocks and TT be the tension in the string. The equations of motion for the left block (m1=1.0 kgm_1 = 1.0\text{ kg}) and the right block (m2=1.0 kgm_2 = 1.0\text{ kg}) are:

m1gsin⁡θ1−T=m1am_1 g \sin \theta_1 - T = m_1 a

T−m2gsin⁡θ2=m2aT - m_2 g \sin \theta_2 = m_2 a

Adding the two equations, we get:

a=m1gsin⁡θ1−m2gsin⁡θ2m1+m2a = \dfrac{m_1 g \sin \theta_1 - m_2 g \sin \theta_2}{m_1 + m_2}

Substituting the given values:

a=1.0×g×(45)−1.0×g×(35)1.0+1.0a = \dfrac{1.0 \times g \times \left(\dfrac{4}{5}\right) - 1.0 \times g \times \left(\dfrac{3}{5}\right)}{1.0 + 1.0}

a=4g5−3g52=g52=g10a = \dfrac{\dfrac{4g}{5} - \dfrac{3g}{5}}{2} = \dfrac{\dfrac{g}{5}}{2} = \dfrac{g}{10}

Answer: g/10g/10
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