Question

A block of mass 5 kg is (i) pushed in case (A) and (ii) pulled in case (B), by a force F = 20 N, making an angle of 30º with the horizontal, as shown in the figures. The coefficient of friction between the block and floor is m = 0.2. The difference between the accelerations of the block, in case (B) and case (A) will be : (g = 10 ms⁻²)
(A) 0.4 ms⁻²
(B) 3.2 ms⁻²
(C) 0 ms⁻²
(D) 0.8 ms⁻²

Answer 1

Option A is correct.... ❤

Answer 2

Answer: let first find the individual acceleration for two cases :

a.) Case 1 : object is pushed

Here, Normal reaction is ,

[ 50 + {20sin(30°)}] = 60N

Friction force is = 60×0.2 = 12N

Pushing force in direction of motion is, 20cos(30°) = 10√3 N = 17.32 N

Net acc. = [ 17.32 - 12 ]/5

= 1.064m/s^2

Case 2 : object is pulled

Normal reaction = 50 - 20sin(30°)

= 40N

Friction force = 0.2× 40 = 8N

Pulling force in direction of motion

= 10cos30° = 17.32N

Net acc. = [17.32 - 8 ]/5 = 1.864m/s^2

So, difference in acceleration is

= 1.864 - 1.064 = 0.8m/s^2

Option d is correct.

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