Determine the force to pull box along a level surface:
A metal box having weight 10KN is pulled along a level surface at the uniform speed by applying horizontal force of 3500N. If another box of 6KN is put on the top of this box, determine the force needed.
Sol.: In first case as shown in the given figure
∑H = 0
µ R = 3500 ...(i)
∑V = 0
R = W = 10KN = 10000 ...(ii)
Putting value of R in the equation (i)
µ = 0.35 ...(iii)
Now consider second case: as shown in the figure
Now the normal reaction is N1,
P - µR1 = 0
P = µ R1 ...(iv)
R_{1} = W = 10KN + 6KN = 16000
R_{1} = 16000 ...(v)
Putting value of R_{1} in the equation (iv)
P = 0.35 × 16000
P = 5600N .......ANS