Laws of motion 3 Flashcards
Can a body remain in state of rest, when external forces are acting on it? Explain your answer.
Yes, if the external forces acting on the body can be represented in magnitude and direction by the sides of a closed polygon taken in the same order.
Name physical situation, where the mass of a body changes with time.
When the body moves with a speed comparable to the speed of light. For example, the mass of a charged particle increases, when it is accelerated in a cyclotron.
When are the two bodies said to possess equal masses?
Ans. If the same force acting on the two bodies produces the same acceleration, then the two bodies must be of equal masses.
Is a bus moving along a circular track, an inertial frame of reference?
No. It is a non-inertial frame of reference.
What can be said about the motion of the vehicle, if a plumb line hanging from its roof drops vertically?
Either the vehicle is at rest or it is moving with constant velocity.
Describe how a man weighing 980 N might be able to slide down a rope that can support a weight of only
755 N.
The man would exert a force of 980 N on the rope, if he grasped it and held firmly. Since the rope would break, if a force greater than 755 N was exerted; he should use the rope only toslow down himself and not to stop completely. Therefore, if the man slides down the rope, so that the frictional force is less than or equal to 755 N, the rope will not break.
Define impending motion
The term impending motion means the motion that would take place under the effect of the appliod force, if friction were absent.
Define rolling friction
In order to keep the body rolling, some force has to be applied. It implies that some friction is there, which opposes the rolling motion and this friction is called rolling friction.
Friction is a necessary evil
Friction, a non-conservative force, is termed a necessary evil due to its advantages and disadvantages. It aids walking, writing, knot-tying, braking, and driving. It’s vital for power transmission and safety measures. However, friction causes wear, heat, energy loss, and fuel consumption, impacting machinery efficiency and lifespan.
Methods to reduce friction
- by proper selection of material
- by polishing
- by lubricating
- by air cushion
- by converting sliding friction into rolling friction
- by streamlining
Why are tyres made of rubber and not iron
It is because the coefficient of friction between rubber and concrete is less than that between iron and the road
Why are wheels made circular?
The rolling friction is less than sliding friction. So wheels are made circular so as to convert sliding friction into a rolling friction.
Why are lubricant used in machines?
When a machine is lubricated, then layers of lubricant to cover the two surfaces moving in contact with each other. The sliding motion no takes place between the two layers of the lubricant rather than the two solid surfaces that is the sliding friction is converted into fluid friction, since fluid friction is much less than sliding friction, the where enter of machine is reduced due to decrease in friction
Is a large brake on a bicycle view more effective than a small one
?
Both large and small bricks are equally effective. It is because, the force of limiting friction is independent of the area of surfaces in contact, so long as the normal reaction remains the same.
