Work Done by Friction

Q.

Statement I: 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 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.
Statement II: The coefficient of friction between the block and the surface decreases with the increase in the angle of inclination.

1. If statement I is true, Statement II is true; Statement II is the correct explanation for Statement I

2. If statement I is true, Statement II is true; Statement II is not correct explanation for Statement I

3. If statement I is true, Statement II is false

4. If statement I is false, Statement II is true

Q. A block of mass $5\text{kg}$ slides down on a rough inclined plane of coefficient of friction $0.75$ having angle of inclination ${37}^{\circ }$ as shown in the figure. Initially if the block is at rest on the top of inclined plane of length $2\text{m}$, then the work done against the friction in moving the block to the bottom of inclined plane is (Take $g=10{\text{m/s}}^2$).

1. $0\text{J}$
2. $5\text{J}$
3. $10\text{J}$
4. $-5\text{J}$

Q.

A large slab of mass 5 kg lies on a smooth horizontal surface, with a block of mass 4 kg lying on top of it. The coefficient of friction between the block and the slab is 0.25. If the block is pulled horizontally by a force of F = 6 N, the work done by the force of friction on the slab, between the instants t=2 s and t=3 s, is (g = 10 m$s^{-2}$)

1. 2.4 J

2. 5.55 J

3. 4.44 J

4. 10 J

Q. Static friction can do non zero work.

1. True
2. False

Q. A block of mass $10\text{kg}$ lies on a rough plane as shown in the figure. A constant force $F$ is applied for $10$ seconds, find out the value of work done by the force $F$.

1. $12000\text{J}$
2. $10000\text{J}$
3. $-6000\text{J}$
4. $0\text{J}$ (because friction is present)

Q. In the arrangement shown in figure $m_A=4.0\text{kg}$ and $m_B=1.0\text{kg}.$ The system is released from rest and block $B$ is found to have a speed $0.3\text{m/s}$ after it has descended through a distance of $1\text{m}$. Find the coefficient of friction between the block $A$ and the table. Neglect friction elsewhere. (Take $g=10m/s^2$)

1. $0.231$
2. $0.501$
3. $0.110$
4. $0.23$

Q. Consider the situation as shown in figure. A constant force acting on the lower blocks produces an acceleration of $4{\text{m/s}}^2.$ The two blocks always move together. Find the work done by static friction on the upper block during displacement $2\text{m}$ of the system.

1. $8\text{J}$
2. Zero
3. $16\text{J}$
4. $10\text{J}$

Q. A body of mass $2\text{kg}$ initially at rest moves under the action of an applied horizontal force of $7\text{N}$ on a table with coefficient of kinetic friction ${\mu }_k=0.1$.
Calculate the work done by kinetic friction in $10\text{sec}(g=9.8{\text{m/s}}^2)$

1. $246.96\text{J}$
2. $-246.96\text{J}$
3. $882\text{J}$
4. $-882\text{J}$

Q. In a figure shown below, the work done by force of friction on the block is

1. Zero
2. Positive
3. Negative
4. cannot be determined

Q.

The work done by kinetic friction on an object is always negative.

1. True

2. False

Q. Static friction can do non zero work.

1. True
2. False

Q. A block of mass $m$ is moving down with constant velocity along an inclined plane of inclination $\theta$. What is the work done by an external force (applied parallel to the inclined plane) in pulling the block up the inclined plane through a height ${}^{\prime }{h}^{\prime }$ with constant velocity?

1. $3mgh$
2. $mgh$
3. $mgh\sin \theta$
4. $2mgh$