Question

a mass of 4 kg moving with 10m/s comes to rest after covering 2m on horizontal surface. Calculate coefficient of friction, work done by frictional force

Answer 1

Answer:

Coefficient of friction = 2.5

Work done by frictional force = -200J

Work done by gravitational force = 0

Explanation:

v2 = u2 + 2as

0 = 102 + 2*a*2

= 100 +4a

-4a = 100

a = -25m/s2

Ffriction = mass * acceleration

= 4 * -25

Ffriction = -100N

We know normal reaction acting on the body = weight of body and weight of body = mg

mg = 4 * 10 = 40N

Ffriction = μ * normal reaction N

μ = Ffriction/N

= 100/40 (since it is coefficient, it doesn’t have a sign)

μ = 2.5

So,

Work done by friction = Ffriction * s

= -100 * 2

Work done by friction = -200J

Work done by gravity = F*s*cos 90

Work done by gravity = 0

Answer 2

Answer:

Mass of the body = 4 kg
Initial velocity = 10 m/s
since the body comes to rest, final velocity = 0 m/s
horizontal displacement = 2 m

using equation of motion v^2 = u^2 + 2as
a = -25m/s^2 (-ve sign indicates body decelerates)

Frictional force = ma = -100 N

μ = | Ff | / N
μ = 2.5

Work done by Frictional force = Force x Displacement = -200 J
Work done by Gravitational force = F.s.cos90 = 0 J