Q. No.Suppose all the surfaces in the previous problem are rough. The direction of friction on B due to A
1. is upward
2. is downward
3. is zero
4. depends on the masses of A and B
Previous problem: Consider the situation shown in the figure. The wall is smooth but the surfaces of A and B in contact are rough.
Previous problem: Consider the situation shown in the figure. The wall is smooth but the surfaces of A and B in contact are rough.
Two cars of unequal masses use similar tyres. If they are moving at the same initial speed, the minimum stopping distance
1. is smaller for the heavier car
2. is smaller for the lighter car
3. is the same for both cars
4. depends on the volume of the car
In order to stop a car in shortest distance on a horizontal road, one should:
| 1. | apply the brakes very hard so that the wheels stop rotating. |
| 2. | apply the brakes hard enough to just prevent slipping. |
| 3. | pump the brakes (press and release). |
| 4. | shut the engine off and not apply brakes. |
A block A kept on an inclined surface just begins to slide if the inclination is 30°. The block is replaced by another block B and it is found that it just begins to slide if the inclination is 40°.
1. mass of A > mass of B
2. mass of A < mass of B
3. mass of A = mass of B
4. All the three are possible
A boy of mass M is applying a horizontal force to slide a box of mass M' on a rough horizontal surface. The coefficient of friction between the shoes of the boy and the floor is µ and that between the box and the floor is µ'. In which of the following cases it is certainly not possible to slide the box?
1. µ < µ’, M < M’
2. µ > µ’, M < M’
3. µ < µ', M'> M’
4. µ > µ', M > M’
Let \(F,F_N\) and \(f\) denote the magnitudes of the contact force, normal force and the friction exerted by one surface on the other kept in contact. If none of these is zero,
| (a) | \( F>F_N \) |
| (b) | \( F>f \) |
| (c) | \( F_N>f \) |
| (d) | \( F_N-f<F<F_N+f\) |
Choose the correct option:
| 1. | (a), (b) and (c) |
| 2. | (a), (b) and (d) |
| 3. | (b), (c) and (d) |
| 4. | All of these |
The contact force exerted by a body A on another body B is equal to the normal force between the bodies. We conclude that
(a) the surfaces must be frictionless
(b) the force of friction between the bodies is zero
(c) the magnitude of normal force equals that of friction
(d) the bodies may be rough but they don’t slip on each other
Choose the correct option:
1. (a) and (b)
2. (b) and (c)
3. (b) and (d)
4. (a) and (c)
Mark the correct statements about the friction between two bodies.
| (a) | static friction is always greater than kinetic friction. |
| (b) | coefficient of static friction is always greater than the coefficient of kinetic friction. |
| (c) | limiting friction is always greater than kinetic friction. |
| (d) | limiting friction is never less than static friction. |
Choose the correct option:
| 1. | (a), (b) and (c) |
| 2. | (b), (c) and (d) |
| 3. | (a) and (d) |
| 4. | (c) and (d) |
A block is placed on a rough floor and a horizontal force \(F\) is applied on it. The force of friction \(f\) by the floor on the block is measured for different values of \(F\) and a graph is plotted between them.
| (a) | The graph is a straight line of slope \(45^{\circ}.\) |
| (b) | The graph is a straight line parallel to the \(F\)-axis. |
| (c) | The graph is a straight line of slope \(45^{\circ}\) for small \(F\) and a straight line parallel to the \(F\)-axis for large \(F.\) |
| (d) | There is a small kink on the graph. |
Choose the correct option:
1. (a) and (b)
2. (b) and (c)
3. (c) and (d)
4. (a) and (d)
Consider a vehicle going on a horizontal road towards the east. Neglect any force by the air. The frictional forces on the vehicle by the road
(a) is towards east if the vehicle is accelerating
(b) is zero if the vehicle is moving with a uniform velocity
(c) must be towards the east
(d) must be towards the west
Choose the correct option:
1. (a) and (b)
2. (a) and (c)
3. (b) and (c)
4. (c) and (d)
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