Question

A 3kg box is pulled along the floor with a force of P=20 N at an angle of 30 degrees. If the box is moving at a constant velocity, calculate the force of friction f, the normal force N and the weight W.

Answer 1

If force is applied at 30 degree with the horizontal

then first we will find the components of force in two directions

`F_x = 20 cos20`

`F_y = 20 sin30`

now we can find normal force by balancing the forces in Y direction

`F_n + Fy = mg`

`F_n + 20 sin30 = 3*10`

`F_n + 10 = 30`

`F_n = 20 N`

now since block is moving with constant speed

so here forces along horizontal plane will be balanced also

`F_x = F_f`

`F_f = 20 cos30`

`F_f = 17.3 N`

Now the weight of the box is defined as

`W = mg`

now plug in all values

`W = 3*10 = 30 N`