Friction and Surface Area of the Object

Q. Two particles having mass m and having equal charge are to be placed on a rough horizontal surface with coefficient of static friction meu at a distance r. Find the minimum charges on each particle so that they remain stationary.

Q. A ball of mass $m$ falls from rest under gravity in a resisting medium (Exerting drag during motion). The resistance force is given by $f=kv$, which can be considered as a friction force offered by the resisting medium. The correct velocity $\left(v\right)$ versus time $\left(t\right)$ graph for body is:

1. 
2. 
3. 
4. 

Q. A block of unknown mass is at rest on a rough horizontal surface. A force $F$ is applied to the block. The graph in the figure shows the acceleration of the block w.r.t the applied force.
The mass of the block and coefficient of friction are $(g=10{\text{m/s}}^2)$

1. $2\text{kg},0.1$
2. $2\text{kg},0.2$
3. can't be determined
4. $1\text{kg},0.1$

Q. The coefficient of static friction maybe
A less than one
B greater than one
C equal to one
D all the above

Q.

Is a large brake on a bicycle wheel more effective than a small one? Explain.?

Q. A cubical wooden box of side $L$ is placed on a horizontal rough surface and the coefficient of static friction between them is $\mu$. Another cubical box of same wood but of length $2L$ is placed on the same surface. Then the coefficient of static friction is

1. $8\mu$
2. $4\mu$
3. $2\mu$
4. $\mu$

Q. Choose the correct statements. The coefficient of static friction depends on
(1) the material of the bodies in contact.
(2) quality of machining of the surface in contact.
(3) presence of foreign matter between the surface.
(4) area of the surfaces in contact.

1. I, II
2. I, II, III
3. I, II, III, IV
   
4. I, III

Q.

state laws of static friction

Q. A body of mass $10\text{kg}$ is kept on a rough horizontal surface. A force of $50\text{N}$ is required to just move the body. If the body is cut into two equal parts and placed one over the other, find the force required to just move the body.

1. $10\text{N}$
2. $25\text{N}$
3. $50\text{N}$
4. $100\text{N}$

Q.

A block is released from a height $h=5m$. After travelling through the smooth curved surface, it moves on the rough horizontal surface through a length $l=8$ $m$ and climbs onto the other smooth curved surface through a height $h^{\prime }$
. If $\mu =0.5$, then $h^{\prime }$ is
$m$.

Q. Two particles having mass m and having equal charge are to be placed on a rough horizontal surface with coefficient of static friction μ at a distance r. Find the minimum charges on each particle so that they remain stationary.

Q. Which of the following statements is false about static friction?

1. It is a self-adjusting force
2. It depends on the external force applied on the body
3. It depends on the area of contact
4. It depends on the surfaces of contact.

Q. Which of the following statements is false about static friction?

1. It is a self-adjusting force
2. It depends on the area of contact
3. It depends on the surfaces of contact.
4. It depends on the external force applied on the body

Q. The coefficient of static friction between two surfaces depend on

1. the nature of surface
2. the shape of the surface in contact
3. the area of contact
4. all of the above

Q.

A capacitor is connected with a battery and stores energy U. After removing the battery, it is connected with another similar capacitor in parallel. The new stored energy in each capacitor will be

1. $\frac{U}{2}$
2. $U$
3. $\frac{U}{4}$
4. $\frac{3U}{2}$

Q. Three capacitors $C_1,C_2$ and $C_3$ are connected to a battery of $6V$ as shown in figure. Find the charges on the three capacitors.

1. $(30\mu C,15\mu C,15\mu C)$
2. $(20\mu C,15\mu C,15\mu C)$
3. $(30\mu C,10\mu C,15\mu C)$
4. $(30\mu C,15\mu C,5\mu C)$

Q. A cubical wooden box of side $L$ is placed on a horizontal rough surface and the coefficient of static friction between them is $\mu$. Another cubical box of same wood but of length $2L$ is placed on the same surface. Then the coefficient of static friction is

1. $8\mu$
2. $4\mu$
3. $2\mu$
4. $\mu$

Q. Suppose a block of mass 1 kg is placed over a rough surface and a horizontal force F is applied on the block as shown in figure. Now, let us see what are the values of force of friction f and acceleration of the block a if the force F is gradually increased. Given that ${\mu }_s=0.5,{\mu }_k=0.4$ and (g= $10m/s^2$).

Q. Three identical capacitors $C_1,C_{2}and{C}_3$ of capacitance $6\mu F$ each are connected to a 12 V battery as shown. Find the charge on each capacitor.

Q.

A capacitor of capacitance 1$\mu$F withstands a maximum voltage of 6 kV, while another capacitor of capacitance 2 $\mu$ F withstands a maximum voltage of 4 kV. If they are connected in series, the combination can withstand a maximum voltage of :

1. $3kV$
2. $6kV$
3. $10kV$
4. $9kV$

Q. A capacitor is charged with a battery and energy stored is $U$. After disconnecting battery another capacitor is of same capacity is connected in parallel with it. Then energy stored in each capacitor is:

1. $U/2$
2. $U/4$
3. $4U$
4. $2U$

Q. A block of mass $10kg$ is moving on a rough surface as shown in the figure. The frictional force acting on the block is

1. $20N$
2. $60N$
3. $40N$
4. $80N$

Q. Which is true for rolling friction $\left({\mu }_r\right)$, static friction $\left({\mu }_s\right)$ and kinetic friction $({\mu }_k$)?

1. ${\mu }_s>{\mu }_r>{\mu }_k$
2. ${\mu }_s<{\mu }_k>{\mu }_r$
3. ${\mu }_s<{\mu }_k<{\mu }_r$
4. ${\mu }_s>{\mu }_k>{\mu }_r$

Q. A small particle slides along a track with elevated ends and a flat central part, as shown in figure. The flat part has a length $3m$, the curved portions of the track are frictionless, but for the flat part, the coefficient of kinetic friction is $\mu =0.2$. The particle is released at a point $A$, which is at a height $h=1.5m$ above the flat part of the track. The position where the particle finally come to rest is:

1. left to mid-point of the flat part
2. right to the mid point of the flat part
3. mid point of the flat part
4. none of these

Q. Assertion :A block of mass $m$ starts moving on a rough horizontal surface with a velocity $v$. It stops due to friction between the block and the surface after moving through a certain distance. The surface is now tilted to an angle of 30${}^{\circ }$ with the horizontal and the same block is made to go up on the surface with the same initial velocity $v$. The decrease in the mechanical energy in the second situation is smaller than that in the first situation. Reason: The coefficient of friction between the block and the surface decreases with the increase in the angle of inclination.

1. Both Assertion and Reason are correct and Reason is the correct explanation for Assertion
2. Both Assertion and Reason are correct but Reason is not the correct explanation for Assertion
3. Assertion is correct but Reason is incorrect
4. Both Assertion and Reason are incorrect

Q. A capacitor $C_1=1.0\mu F$ is charged up to a voltage $V=60V$ by connecting it to battery $B$ through switch (1), Now $C_1$ is disconnected from battery and connected to a circuit consisting of two uncharged capacitors $C_2=3.0\mu F$ and $C_3=6.0\mu F$ through a switch (2) as shown in the figure. The sum of final charges on $C_2$ and $C_3$ is:

1. $40\mu C$
2. $36\mu C$
3. $20\mu C$
4. $54\mu C$

Q. A ban rolls without sliding over a rough horizontal floor with velocity $V_0=7m/s$ towards a smooth vertical wall. If coefficient of restitution between the wall and the ball is $e=07.$ Calculate velocity v of the ball long after the collision.

Q. A network of four 20 $\mu F$ capacitors is connected to a 600 V supply as shown in the figure. The charge on capacitors $C_1$ and $C_4$ are

1. $4\times {10}^{-3}C,12\times {10}^{-3}C$
2. $6\times {10}^{-3}C,12\times {10}^{-3}C$
3. $2\times {10}^{-3}C,4\times {10}^{-3}C$
4. $3\times {10}^{-3}C,2\times {10}^{-3}C$

Q. A particle of mass m rests on a horizontal floor with which it has a coefficient of static friction $\mu$. If is desired to make the body move by applying the minimum possible force F. Find the magnitude of F and the direction in which it has to be applied.

Q. A block A of mass 2kg rests on another block B of mass 8kg which rests on a horizontal floor. The coefficient of friction between A and B is 0.2 while that between B and floor is 0.5. If a horizontal force F of 25 N is applied on the block B, find the force of friction between A and B.

1. 0
2. $25N$
3. $4N$
4. $50N$