What is the acceleration of the block and trolley system shown in a Figure, if the coefficient of kinetic friction between the trolley and the surface is $0.04$? What is the tension in the string ? (Take $g = 10\; m s^{-2}$). Neglect the mass of the string.
Answer As the string is inextensible, and the pully is smooth, the $3\, kg$ block and the $20 \,kg$ trolley both have same magnitude of acceleration. Applying second law to motion of the block (Fig. $5.12( b ))$ $30-T=3 \,a$
Apply the second law to motion of the trolley
$T-f_{ k }=20 \,a$
Now $\quad f_{k}=\mu_{k} N$
Here $\mu_{k} =0.04$
$N =20 \times 10$
$=200\, N$
Thus the equation for the motion of the trolley is $T-0.04 \times 200=20 \,a$ Or $T-8=20 \,a$
These equations give $a=\frac{22}{23} \,m s ^{-2}=0.96 \;m s ^{-2}$
and $T=27.1 \,N$
A block is projected with speed $20 \,m / s$ on a rough horizontal surface. The coefficient of friction $(\mu)$ between the surfaces varies with time $(t)$ as shown in figure. The speed of body at the end of $4$ second will be ............ $m / s$ ( $g=$ $10 \,m / s ^2$ )
A body is pulled along a rough horizontal surface with a velocity $6\,m/s$. If the body comes to rest after travelling $9\,m$ , then coefficient of sliding friction, is- (Take $g = 10\,m/s^2$ )
$10\, kg$ block is placed as shown, if $F = 50$ newton find friction force ............ $N$
A bag is gently dropped on a conveyor belt moving at a speed of $2\,m / s$. The coefficient of friction between the conveyor belt and bag is $0.4$ Initially, the bag slips on the belt before it stops due to friction. The distance travelled by the bag on the belt during slipping motion is $.....m$ [Take $g=10\,m / s ^{-2}$ ]
For a given mass rolling friction is how many times static friction and kinetic friction?