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Time Taken for Block to Slide Down Moving Wedge

A wedge YY with mass of 10 kg10\text{ kg} and all frictionless surfaces and the inclined surface making 3737^\circ with horizontal. A block XX with mass 2 kg2\text{ kg} is placed at the highest point of the wedge as shown in figure is at rest. At t=0t = 0 wedge (YY) is pulled toward right with constant force (ff) of 24 N24\text{ N}. Taking the block XX at rest at t=0t = 0, the time taken by it to slide down 8.8 m8.8\text{ m} on the slope, while YY is on the move, is ______ s. (take tan(37)=3/4\tan (37^\circ) = 3/4 and g=10 m/s2g = 10\text{ m/s}^2)

Question Diagram 1

Options

A

22

Correct
B

44

C

2\sqrt{2}

D

222\sqrt{2}

Topics & Concepts

Step-by-Step Solution

To find the time taken by block XX to slide down the wedge YY, we analyze the motion of the system using Newton's laws of motion.

1. Given Data

  • Mass of wedge YY, M=10 kgM = 10\text{ kg}
  • Mass of block XX, m=2 kgm = 2\text{ kg}
  • Pulling force, f=24 Nf = 24\text{ N}
  • Angle of inclination, θ=37    sin37=0.6,cos37=0.8\theta = 37^\circ \implies \sin 37^\circ = 0.6, \cos 37^\circ = 0.8
  • Distance to slide along the slope, S=8.8 mS = 8.8\text{ m}
  • Acceleration due to gravity, g=10 m/s2g = 10\text{ m/s}^2

2. Horizontal Acceleration of the Wedge System

The total horizontal force f=24 Nf = 24\text{ N} acts on the system consisting of the wedge and the block. The horizontal acceleration aa of the system is given by:

a=fM+ma = \frac{f}{M + m}

Substituting the given values:

a=2410+2=2412=2 m/s2a = \frac{24}{10 + 2} = \frac{24}{12} = 2\text{ m/s}^2


3. Motion of Block XX Relative to Wedge YY

In the non-inertial reference frame of the accelerating wedge YY:

  1. The component of acceleration due to gravity along the inclined plane (downwards) is: ag,=gsin37=10×0.6=6 m/s2a_{g, \parallel} = g \sin 37^\circ = 10 \times 0.6 = 6\text{ m/s}^2

  2. Since the wedge accelerates to the right with acceleration a=2 m/s2a = 2\text{ m/s}^2, block XX experiences a pseudo acceleration of a=2 m/s2a = 2\text{ m/s}^2 to the left. The component of this pseudo acceleration opposing the motion down the incline is: apseudo,=acos37=2×0.8=1.6 m/s2a_{\text{pseudo}, \parallel} = a \cos 37^\circ = 2 \times 0.8 = 1.6\text{ m/s}^2

Thus, the net relative acceleration ara_r of block XX sliding down the incline is:

ar=gsin37acos37a_r = g \sin 37^\circ - a \cos 37^\circ ar=61.6=4.4 m/s2a_r = 6 - 1.6 = 4.4\text{ m/s}^2


4. Calculation of Time Taken

Using the kinematic equation for motion along the incline with initial relative velocity ur=0u_r = 0:

S=12art2S = \frac{1}{2} a_r t^2

Substitute S=8.8 mS = 8.8\text{ m} and ar=4.4 m/s2a_r = 4.4\text{ m/s}^2:

8.8=12×4.4×t28.8 = \frac{1}{2} \times 4.4 \times t^2 8.8=2.2×t28.8 = 2.2 \times t^2 t2=8.82.2=4t^2 = \frac{8.8}{2.2} = 4 t=2 st = 2\text{ s}

Thus, the time taken by block XX to slide down 8.8 m8.8\text{ m} on the slope is 2 s2\text{ s}.

Time Taken for Block to Slide Down Moving Wedge | Physics PYQ Solution - JEE Challenger