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A block of mass 2 kg is on a horizontal ...

A block of mass 2 kg is on a horizontal surface. The coefficient of static & kinetic frictions are 0.6 & 0.2 The minimum horizontal force required to start the motion is applied and if it is continued, the velocity acquired by the body at the end of the 2nd second is (g=`10ms^2`)

A

`8 ms^(-1)`

B

`4 ms^(-1)`

C

`2 ms^(-1)`

D

zero

Text Solution

AI Generated Solution

The correct Answer is:
To solve the problem step by step, we will follow the outlined process below: ### Step 1: Identify the Given Data - Mass of the block, \( m = 2 \, \text{kg} \) - Coefficient of static friction, \( \mu_s = 0.6 \) - Coefficient of kinetic friction, \( \mu_k = 0.2 \) - Acceleration due to gravity, \( g = 10 \, \text{m/s}^2 \) ### Step 2: Calculate the Normal Force The normal force \( N \) acting on the block is equal to its weight since it is on a horizontal surface: \[ N = mg = 2 \, \text{kg} \times 10 \, \text{m/s}^2 = 20 \, \text{N} \] ### Step 3: Calculate the Maximum Static Friction The maximum static friction force \( f_s \) that needs to be overcome to start the motion is given by: \[ f_s = \mu_s \cdot N = \mu_s \cdot mg \] Substituting the values: \[ f_s = 0.6 \cdot 20 \, \text{N} = 12 \, \text{N} \] ### Step 4: Determine the Minimum Force Required to Start Motion The minimum horizontal force \( F \) required to start the motion is equal to the maximum static friction: \[ F = f_s = 12 \, \text{N} \] ### Step 5: Calculate the Kinetic Friction Force Once the block starts moving, the kinetic friction force \( f_k \) acting on it is given by: \[ f_k = \mu_k \cdot N = \mu_k \cdot mg \] Substituting the values: \[ f_k = 0.2 \cdot 20 \, \text{N} = 4 \, \text{N} \] ### Step 6: Calculate the Net Force Acting on the Block The net force \( F_{net} \) acting on the block after it starts moving is: \[ F_{net} = F - f_k = 12 \, \text{N} - 4 \, \text{N} = 8 \, \text{N} \] ### Step 7: Calculate the Acceleration of the Block Using Newton's second law, the acceleration \( a \) of the block can be calculated as: \[ a = \frac{F_{net}}{m} = \frac{8 \, \text{N}}{2 \, \text{kg}} = 4 \, \text{m/s}^2 \] ### Step 8: Calculate the Velocity After 2 Seconds Using the equation of motion, the final velocity \( v \) after time \( t = 2 \, \text{s} \) can be calculated using: \[ v = u + at \] where \( u \) (initial velocity) is 0 (since the block starts from rest): \[ v = 0 + (4 \, \text{m/s}^2 \cdot 2 \, \text{s}) = 8 \, \text{m/s} \] ### Final Answer The velocity acquired by the body at the end of the 2nd second is: \[ \boxed{8 \, \text{m/s}} \]
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