Sliding penny

A coin of mass 3 g 3~\mbox{g} slides horizontally on the surface of a table. The frictional force exerted on the penny is 0.0147 N 0.0147~\mbox{N} . What is the coefficient of friction between the table and the penny?

Details and assumptions

  • The acceleration of gravity is 9.8 m/s 2 -9.8~\mbox{m/s}^2 .


The answer is 0.5.

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10 solutions

Frictional force can be expressed as

F f = μ N Ff= μ · N

N = m g N = m · g

where

F f = f r i c t i o n a l Ff = frictional f o r c e ( N , l b ) force (N, lb)

μ = f r i c t i o n a l μ = frictional c o e f f i c i e n t coefficient s t a t i c static o r or k i n e t i c kinetic ( μ s , μ k ) (μs, μk)

N = n o r m a l N = normal f o r c e force ( N , l b ) (N, lb)

m = m a s s m = mass o f of t h e the o b j e c t object ( k g ) (kg)

g = a c c e l e r a t i o n g = acceleration o f of g r a v i t y gravity ( 9.8 m / s 2 ) (9.8 m/s^{2})

Input the number..

N = 0.003 k g 9.8 m / s 2 N = 0.003 kg · 9.8m/s^{2}

N = 0.0294 N N = 0.0294 N

0.0147 N = μ 0.0294 N 0.0147 N = μ · 0.0294 N

μ = 0.5 μ =0.5

HAHAHA forgot to convert the gram

Rahim Yusuf - 7 years, 10 months ago
Ryan Carson
Aug 11, 2013

The formula for the Coefficient of Friction is μ = F f F N \mu = \frac{F_f}{F_N} where:

  • F f = F_f = Force of Friction, and

  • F N F_N is the Normal force.

Since the penny is sliding horizontally (perpendicular to the Force of Gravity), F N = F g = m a F_N = F_g = ma

Using mass in kg, and g as 9.8, we find:

μ = 0.0147 0.003 × 9.8 = 0.5 \mu = \frac{0.0147} {0.003 \times 9.8} = 0.5

thank u

Arnav Rupde - 7 years, 9 months ago
Indrajeet Singh
Aug 18, 2013

frictional force=coefficient of friction * normal reaction.

Oliver Welsh
Aug 15, 2013

The coefficient of friction ( u u ), can be caluclated using the equation:

u = F f m g u = \frac{F_f}{m \cdot g}

Using the given values, we get:

u = 0.0147 0.003 9.8 = 0.5 u = \frac{0.0147}{0.003 \cdot 9.8} = \fbox{0.5}

Kartik Goel
Aug 15, 2013

f=uR u= coefficient of friction R=reaction force =mg m=0.003 kg g=9.8 m/s sq. 0.0147=u * 0.003 * 9.8 u=0.5

Michael Tang
Aug 14, 2013

The formula for friction is f = k N , f = kN, where k k is the desired coefficient of friction and N N is the normal force acting on the object. In this case, the normal force is gravity, because the coin is sliding horizontally. Thus, the normal force has magnitude 0.003 g 0.003g newtons. Substituting, we get 0.0147 = 0.003 g N . 0.0147 = 0.003g\cdot N. Solving for N , N, we get N 0.5 . N \approx \boxed{0.5}.

Sahil Goyal
Aug 14, 2013

as coefficient of friction is [(frictional force exerted)/(weight of object)] So,[(0.0147)/(0.003*9.8)]=0.5

Santanu Banerjee
Aug 13, 2013

Since friction is kinetic , thus

u m g = F = 0.0147 N

m = 0.003 kg

Putting the values and on solving we get u = 0.5 which is the coefficient of kinetic friction

Shubham Chaudhary
Aug 12, 2013

F=Nu(meu) u=mg 3*9.8=29.4 kgm/s2 F=Nu F/N=u 0.0147/29.4=0.5

The-Third Eye
Aug 12, 2013

Frictional force can be expressed as

Ff = μ · N        (1)

where

Ff = frictional force (N, lb)

μ = static (μs) or kinetic (μk) frictional coefficient

N = normal force (N, lb)

N=mg

so u=F/mg

u=0.0147/3 9.8 10^-3 = 0.5

The coefficient of friction equal 0.5

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