# PhysicsMechanics- friction

#### Shah 72

##### Member
A book of mass 1.3 kg is on a plank of wood which is held at 16 degree to the horizontal. The coefficient of friction between the book and the plank is 0.45.
Find the size of the frictional force.
Iam getting the ans by using the formula F= coefficient of friction ×R
5.62N but the textbook ans is 3.58N.
Pls help

#### skeeter

##### Well-known member
MHB Math Helper
using 10 for g ...

$f = \mu \cdot mg\cos{\theta} = 5.62 \, N$

an aside ... since you're using a calculator anyway, why not use 9.8 for g? g = 10 is normally used when calculations are done by hand.

#### Shah 72

##### Member
using 10 for g ...

$f = \mu \cdot mg\cos{\theta} = 5.62 \, N$

an aside ... since you're using a calculator anyway, why not use 9.8 for g? g = 10 is normally used when calculations are done by hand.
Thank you!