Question

A 1 Kg object is on a horizontal surface and moves as it is being pulled by a string with tension 3.4N. The string is kept at 45 degrees with the vertical (north-east direction). The kinetic friction coefficient between object and floor is 0.2. Find the work done by friction on the object as the object moves horizontally 1m.

Answer 1

Here form the condition of dynamic equilibrium we have,

Fnet = Tcos45° - mgUk

= 3.4 × Cos45° - 1 ×9.8×0.2 = 0.4441 N

So here work done on the object will be,

W = 0.4441 × 1 = 0.4441 J

Here only the horizontal component of the forces will contribute in work done because the other component make work zero.

Now Work done by the friction here is given as,

Wf = Ff × d = 1 × 9.8 × 0.2 × 1 × (Cos180°) = - 1.96 J

Hence wrok done by fiction on the object will be - 1.96 J

Here negative sign shows that the applied force and distance travelled is in opposite direction.