Question

A force of 60N accelerates a 40N block at 8m/s2. what is the force of friction

Answer 1

F = applied force on the block = 60 N

W = weight of the block = 40 N

a = acceleration of the block in horizontal direction = 8 m/s²

f = frictional force acting in opposite direction of applied force = ?

m = mass of the block

g = acceleration due to gravity = 9.8 m/s²

mass of the block is given as

m = W/g

m = 40/9.8

m = 4.08 kg

from the force diagram , force equation for the motion of the block is given as

F - f = ma

inserting the values

60 - f = (4.08) (8)

60 - f = 32.5

f = 60 - 32.5

f = 27.5 N

hence the force of friction is 27.5 N

Answer 2

weight of the block is given as 40 N

so we have

mg = 40 N

m* 9.8 = 40

`m = (40)/(9.8)`

`m = 4.1 kg`

now by Newton's II law we know that

`F - F_f = ma`

given that

F = 60 N

`F - F_f = ma`

`60 - F_f = 4.1*8`

`F_f = 60 - 4.1*8`

`F_f = 27.2 N`

so friction force will be 27.2 N