Q: A circular road of radius r is banked for a speed $ \mathbf{v}=40 \mathrm{km} / \mathrm{hr} . $ A car of mass $ \mathrm{m} $ attempts to go on the circular road. The friction coefficient between the tyre and the road is negligible.

If the car turns at the correct speed of $ 40 \mathrm{km} / \mathrm{hr} $, the force by the road on the car is greater than mg as well as greater than $ m v^{2} / r $. For a frictionless banked curve at the design speed, the road’s force is the normal reaction. Its vertical component balances weight, while its horizontal component provides centripetal force. Because the normal is tilted, its magnitude must exceed each component, so it is greater than both mg and mv^2/r.

Q: "I is smooth wall, as shown in the diagram, making a variable angle $ \theta $ with the horizontal floor. There is no friction with the vertical wall. At which angle $ \theta $ will the normal force exerted by the floor upwards be at its maximum? Do not consider any motion by the plank

When $ \theta=45.0^{\circ} $. For a stationary plank, the forces must balance in both directions and in torque. The wall’s horizontal reaction and the floor’s vertical normal depend on the angle, and the floor normal is maximized when the geometry makes the torque arm balance most strongly at 45°.

Question 1

$ g c m s^{-2} $ is also known as

Accepted Answer

dyne. In the CGS system, force is measured in dyne. A dyne is defined as the force needed to accelerate 1 gram by 1 cm/s², so its unit form is g·cm·s⁻².

Question 2

The coefficient of limiting friction between the surfaces of contact is the ratio of the $ \ldots $. friction to the normal reaction

Accepted Answer

sliding. Limiting friction is the maximum friction available just before slipping begins, and it is defined as the ratio of this friction to the normal reaction. Among the choices, this corresponds to sliding friction in the sense of impending motion between surfaces.

Question 3

Point where whole weight of body acts vertically is called

Accepted Answer

center of gravity. The whole weight of a body is the resultant gravitational force, and it is considered to act through the center of gravity. This is the point where the body’s total weight can be treated as concentrated vertically.

Question 4

In a physical balance working on the principle of moments, when $ 5 \mathrm{mg} $ weight is placed on the left plan, the beam becomes horizontal. Both the empty pans of the balance are of equal mass. Which of the following statements is correct?

Accepted Answer

Left arm is shorter than the right arm.. Since the pans are equal, the beam balances only when the moments about the pivot are equal. A 5 mg mass on the left achieving balance means the left side must have the shorter arm, so a smaller force can match the moment of the right side's longer arm.

Question 5

A box is placed on an inclined plane and has to be pushed down. The angle of inclination is :

Accepted Answer

More than the angle of friction. A box will move down the plane only when the component of its weight along the plane exceeds the maximum static friction. That requires the inclination angle to be greater than the angle of friction, since at equality the body is just on the verge of slipping.

Question 6

A rubber ball of mass $ 4 \mathrm{kg} $ has the same diameter as a plastic ball of mass 0.5 kg. Both the balls are dropped simultaneously from the roof of a building.When they are $ 8 \mathrm{m} $ above the ground,they have the same

Accepted Answer

Acceleration. If air resistance is neglected, both balls are in free fall and experience the same gravitational acceleration, g. Their masses differ, so their kinetic energy, potential energy, and momentum are not the same at that height.

Question 7

A circular road of radius r is banked for a speed $ \mathbf{v}=40 \mathrm{km} / \mathrm{hr} . $ A car of mass $ \mathrm{m} $ attempts to go on the circular road. The friction coefficient between the tyre and the road is negligible.

Accepted Answer

If the car turns at the correct speed of $ 40 \mathrm{km} / \mathrm{hr} $, the force by the road on the car is greater than mg as well as greater than $ m v^{2} / r $. For a frictionless banked curve at the design speed, the road’s force is the normal reaction. Its vertical component balances weight, while its horizontal component provides centripetal force. Because the normal is tilted, its magnitude must exceed each component, so it is greater than both mg and mv^2/r.

Question 8

"I is smooth wall, as shown in the diagram, making a variable angle $ \theta $ with the horizontal floor. There is no friction with the vertical wall. At which angle $ \theta $ will the normal force exerted by the floor upwards be at its maximum? Do not consider any motion by the plank

Accepted Answer

When $ \theta=45.0^{\circ} $. For a stationary plank, the forces must balance in both directions and in torque. The wall’s horizontal reaction and the floor’s vertical normal depend on the angle, and the floor normal is maximized when the geometry makes the torque arm balance most strongly at 45°.

Question 9

A fly strikes the windshield of a moving truck as shown. What can you say about the forces: the force on the fly and the force on the truck.

Accepted Answer

Force on the fly = Force on the truck. When the fly hits the truck, each exerts a force on the other that is equal in magnitude and opposite in direction. The fly is damaged more because its much smaller mass gives it a much larger acceleration, not because the force is larger.

Question 10

Suppose your writing desk is tilted a little, a book kept on it starts sliding down. The direction of frictional force acting on it is

Accepted Answer

upwards. As the book slides downward, friction opposes that motion. Therefore, the frictional force on the book acts upward along the incline.

Question 11

The motion of centre of mass depends on

Accepted Answer

total external forces. The centre of mass of a system accelerates according to the net external force acting on the system. Internal forces occur in equal and opposite pairs, so they do not change the motion of the centre of mass.

Question 12

A 50 gram bead slides on a frictionless wire as shown above. At what point on the wire will the bead come to a complete stop? The initial speed at $ C $ is $ \sqrt{2 g h} $

Accepted Answer

Point D E. Point E. Because the wire is frictionless, mechanical energy is conserved. The bead’s initial kinetic energy at C is $\tfrac12 mv^2 = \tfrac12 m(2gh)=mgh$, so it will come to rest after rising by a vertical height of $h$ above C.

Question 13

In a hydraulic lift, used at a service station the radius of the large and small piston are in the ratio of $ 20: 1 . $ What weight placed on the small piston will be sufficient to lift a car of mass 1500 kg?

Accepted Answer

37.5 kgg $ g $. In a hydraulic lift, the pressure transmitted through the fluid is equal, so force is proportional to piston area. Since area scales as radius squared, a 20:1 radius ratio gives a 400:1 area ratio, making the needed small-piston force 1500/400 of the car’s weight.

Question 14

There are 3 balls of same shape and size made of wood, iron and plastic. Which one of them would have highest inertia?

Accepted Answer

Iron. Inertia is the resistance of an object to changes in its state of motion, and it increases with mass. Since the balls have the same size and shape, the iron ball has the greatest mass, so it has the highest inertia.

Question 15

Assertion Pulling a lawn roller is easier than pushing it. Reason pulling decreases the apparent weight as the vertical component of the pulling force acts upward.

Accepted Answer

Both Assertion and Reason are correct and Reason is the correct explanation for Assertion.. Pulling a roller usually has an upward component, which reduces the normal reaction and therefore the frictional force. Pushing tends to add a downward component, increasing the normal reaction and making motion harder.

Question 16

If a man is walking, then the direction of friction is:

Accepted Answer

opposite to direction of motion. When a person walks, the foot pushes the ground backward, and the ground exerts friction on the foot forward to prevent slipping. Thus, the friction on the man acts opposite to the backward push of the foot and supports forward motion.

Question 17

Fill in the blanks Dynamic Fluid friction is the sliding friction of solids.

Accepted Answer

lower than. Dynamic fluid friction (viscous resistance) is generally smaller than the friction encountered when two solid surfaces slide. Fluids deform and flow, so they usually offer less resistance than solid-on-solid contact.

Question 18

Which quantity of a two particles system depend only on the separation between the two particles?

Accepted Answer

Potential energy. Potential energy in a two-particle system is a function of their relative separation, because it comes from the interaction between the particles. Kinetic and total mechanical energy also depend on motion, so they are not determined only by distance.

Question 19

Fill in the blank. Pressure is inversely proportional to

Accepted Answer

area. Pressure is defined as force per unit area, so when force stays the same, increasing area makes pressure decrease. That means pressure varies inversely with area.

Question 20

Which of the following factors affect friction?

Accepted Answer

All of the above. Friction is influenced by the nature of the surfaces in contact, the normal force or weight pressing them together, and in many practical situations the motion/speed conditions. Since each listed factor can affect friction, the correct choice is the one that includes all of them.

NEET Physics: Mechanics questions with solutions

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