question_answer

A block slides with a velocity of 10 m/s on a rough horizontal surface. It comes to rest after covering a distance of 50 m. If g is \[10\text{ }m/{{s}^{2}},\] then the coefficient of dynamic friction between the block and surface is:

A)  1                                            

B)  10

C)  2                                            

D)  0.1

Correct Answer: D

Solution :

                From equation of motion, we have \[{{v}^{2}}={{u}^{2}}+2as\] where v is final velocity, u the initial velocity, a the acceleration and s the displacement. Given,\[v=0\](block stops),\[u=10\text{ }m/s,\]            \[s=50\text{ }m\] \[\therefore \] \[0-{{10}^{2}}=2\times a\times 50\] \[\Rightarrow \]               \[a=-1\text{ }m/{{s}^{2}}=ug\] \[\Rightarrow \]               \[\mu =\frac{1}{10}=0.1\]