Finding Friction's Direction

Q.

What is limiting friction and its laws?

Q. A uniform solid sphere rolls on a horizontal surface at 20 ms–1. It then rolls up an incline having an angle of inclination at 30º with the horizontal If the friction losses are negligible, the value of height h above the ground where the ball stops is : (1) 14.3 m (2) 28.6 m (3) 57.2 m (4) 9.8 m

Q.

What is the coefficient of friction when a cylinder rolls down without slipping on an inclined plane?

1. 

2. 

3. 

4. 

Q. Assertion :- For an isolated system mechanical energy is conserved. Reason :- Kinetic frictional force is absent for isolated system

Q.

A block of mass 1kg is placed on the floor. The coefficient of static friction is 0.2. If a force of 1N is applied to the block, the force of friction is

1. 1N

2. 0

3. varies with the area of contact of the block

4. 2N

Q. Which of the following is incorrect about Kinetic friction?

1. It is non conservative force
2. It is a pseudo force.
3. It opposes relative velocity
4. During closed path work done is non zero

Q.

Two blocks of masses $m_1=m_2=m$ are connected by a string of negligible mass which passes over a frictionless pulley fixed on the top of an inclined plane as shown in the figure. When the angle of inclination $\theta ={30}^{\circ }$, the mass $m_1$ just begins to move up the inclined plane. What is the coefficient of friction between block$m_1$ and the inclined plane?

1. $\frac{1}{\sqrt{2}}$

2. $\frac{1}{2\sqrt{2}}$

3. $\frac{1}{\sqrt{3}}$

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

Q. What is meant by banking of roads. Obtain an expression for the maximum speed with which a vehicle can safely negotiate a curved road banked at an $\theta$ consider the friction is negligible.

Q. A given object takes n times as much time to slidedown a 45^° rough incline as it takes to slide downa perfectly smooth 45^° incline. The coefficient ofkinetic friction between the object and the inclineis given by :

Q. Two small blocks slide without losing contact with the surface along two frictionless tracks 1 & 2, starting at the same time with same initial velocity v. Track 1 is perfectly horizontal while track 2 has a dip in the middle as shown in the figure. Which body will reach the finish line first?

Q.

The upper half of an inclined plane of inclination q is perfectly smooth while the lower half is rough. A body starting from the rest at top comes back to rest at the bottom if the coefficient of friction for the lower half is given by

1. m = sin q

2. m = cot q

3. m = 2 cos q

4. m = 2 tan q

Q. A uniform solid sphere rolls on a horizontal surface at 20 ms–1. It then rolls up an incline having an angle of inclination at 30º with the horizontal If the friction losses are negligible, the value of height h above the ground where the ball stops is : (1) 14.3 m (2) 28.6 m (3) 57.2 m (4) 9.8 m

Q. If you pull a tablecloth expertly from between a bowl and table, the directions of friction between the tablecloth and the table, and, between the tablecloth and the bowl is same.

1. False
2. True

Q. A body of mass $10\text{kg}$ lies on a rough inclined plane of inclination $\theta ={\sin }^{-1}\frac{3}{5}$ with the horizontal. When a force of $30\text{N}$ is applied on the block parallel to and upward the plane, the total reaction by the plane on the block is nearly along (take $g=10m{s}^{-2}$)

1. $OA$
2. $OB$
3. $OC$
4. $OD$

Q. A box of mass $\text{8 kg}$ is placed on a rough inclined plane of angle $\theta$. Its downward motion can be prevented by applying an upward pull $F$ and it can be made to slide upwards(constant speed) by applying a force $2F$. The coefficient of friction between the box and the inclined plane is

1. $\frac{\tan \theta }{3}$
2. $3\tan \theta$
3. $\tan \frac{\theta }{3}$
4. $2\tan \theta$

Q.

A girl is standing on ground near a horizontally moving conveyor belt. She throws her suitcase horizontally. Such that the initial velocity of suitcase relative to stationary girl is along dotted line shown in top view of conveyor belt.

Which of the following arrows represents the direction of friction on the bag at the initial moment.

1. Arrow A

2. Arrow B

3. Arrow C

4. Arrow D

Q. A tire rolls on a flat road with constant angular velocity $\omega$ (in counter clockwise direction) and velocity $v$ (towards left). If $v>\omega R$, in which direction does the friction from the road act on the tire?

1. Towards left
2. Towards right
3. Friction does not act on the tire
4. Can't say

Q. A block of mass $m$ is on an inclined plane of angle $\theta$. The coefficient of friction between the block and the plane is $\mu$ and $\tan \theta >\mu$. The block is held stationary by applying a force $P$ parallel to the plane. The direction of force pointing up the plane is taken to be positive. As $P$ is varied from $P_1=mg(\sin \theta -\mu \cos \theta )$ to $P_2=mg(\sin \theta +\mu \cos \theta )$, the frictional force $f$ versus $P$ graph will look like

1. 
2. 
3. 
4. 

Q. Two blocks of masses $m_1$ and $m_2$ are connected with a massless unstretched spring and placed over a plank moving with an acceleration $a$ as shown in the figure. The coefficient of friction between the blocks and the platform is $\mu$.

1. Spring will be stretched if $a>\mu g$
2. Spring will be compressed if $a\le g$
3. Spring will neither be stretched nor be compressed for $a\le g$
4. Spring will be in its natural length under all conditions