Question

A 3.5kg block is pushed along a horizontal floor by a force F of magnitude 15N at an angle 40°W horizontal. The coefficient of kinetic friction between the block and the floor is 0.25. Calculate the magnitude of:

(a) frictional force on the block from the floor

(b) the block's acceleration

Answer 1

The Newton's second law says

$$ma=F\cos40^\circ-F_f$$

and

$$N=mg-F\sin40^\circ\\ =3.5*9.8-15\sin40^\circ=24.7\:\rm N$$

Hence:

(a) frictional force on the block from the floor

$$F_f=\mu N=0.25*24.7=6.2\:\rm N$$

(b) the block's acceleration

$$a=(15\cos40^\circ-6.2)/3.5=1.5\:\rm m/s^2$$