PLEASE ANSWER THE FOLLOWING QUESTIONS :
> Q#1:
A pencil is just balanced at it's tip whatis it's state of equilibrium? Give answer with reason.
> Q#2:
Why it is assumed that a gravitational feild exists all astound the earth?
> Q#3:
For a body of mass 'm' moving in a circle of radius 'r' , if it's velocity is halved what will be the effect of it in the value of centripetal force.
> Q#4:
When a person takes a bucket to some distance, work done by him is zero. Why?
> Q#5:
How effectiveness of small force is increased when action area of force is reduced?
> Q#6:
Why we feel cool after perspiration of sweating?
> Q#7:
Write the name of three factors on which evaporation depends?
> Q#8:
A cup of hot tea becomes cold after some time. Why ?
> Q#9:
Differentiate between or what is the relation between g and G.
> Q#10:
Why is the base of vehicle made wide?
> Q#11:
Can a body moving at constant speed have an acceleration?
> Q#12:
Friction is a necessary evil. Why?
> Q#13:
Two children are sitting on a see-saw such that they cannot swing. What is the net torque in this situation? Explain your answer.
> Q#14:
What is the relation between stability and position of centre of mass?
> Q#15:
How can you say that gravitational force is a field force?
> Q#16:
Can a small child play with a fat child on see-saw? Briefly explain how?
> Q#17:
Why is water used in cooling systems of automobiles?
> Q#18:
What are the factors in which thrust of a liquid depends?
> Q#19:
With what force an apple weighing 1N attracts the earth?
> Q#20:
What is the role of center if gravity/mass in rotational motion?
Answers
Answer:
A pencil balanced at its tip with centre of gravity G at the highest position will be left, the pencil will topple over weight acting at G about its tip and fall down. This is called the unstable equilibrium.
A gravitational field is a model used to explain the influence that a massive body extends into the space around itself producing a force on another massive body..
1. Pencil balanced at its tip with centre of gravity G at the highest position will be left, the pencil will topple over weight acting at G about its tip and fall down. This is called the unstable equilibrium.
2. A gravitational field is a model used to explain the influence that a massive body extends into the space around itself producing a force on another massive body.. In its original concept, gravity was a force between point masses.
3. If the velocity is halved then centripetal force decreases by 4 times.
4. Work done by the force of gravity on the object is zero. Force of gravity acts in the vertical downward direction and the distance covered the of force, the horizontal direction. As there is no displacement in th hence the work done is zero.
5. The force is proportional to the area, for if we increase the area but keep the number of molecules per cubic centimeter the same, we increase the number of collisions with the piston in the same proportion as the area was increased.
more area = more space = more free for molecules = less pressure = less force
6. The sweat leaves your skin through tiny holes called pores. When the sweat hits the air, the air makes it evaporate. As the sweat evaporates off your skin, you cool down.
7. The rate of evaporation depends on the liquid's exposed surface area , the humidity of surroundings and the temperature.
8. The hot tea is at a higher temperature than the surroundings. The heat flows from hot objects to cold objects.The nearby air molecules will collide with the tea in the cup and take away its heat.
9. The constant of proportionality, G, is the gravitational constant.(g) ,which is the local gravitational field of Earth .
10. Vehicles are made wide to lower their center of gravity this helps in handling and makes it harder to roll the vehicles over in an accident.
11. If a body is moving with constant speed in a circle, then yes, that body has acceleration.
12. Frictional force causes a lot of losses in general upkeep and wear and tear of machinery. Hence it is considered as a evil.
13. Frictional force causes a lot of losses in general upkeep and wear and tear of machinery. Hence it is considered as a evil.
14. The position of the centre of gravity of an object affects its stability. The lower the centre of gravity (G) is, the more stable the object. The higher it is the more likely the object is to topple over if it is pushed.
15. A gravitational field is the force field that exists in the space around every mass or group of masses. This field extends out in all directions, but the magnitude of the gravitational force decreases as the distance from the object increases.
16. A small child has less force than a fat one. So , the distance from the pivot of the seesaw should be increased for the small child so that the moment of force or torque is increased. Hence distances have to be adjusted so that sum of clockwise moments matches the sum of anti clockwise moments.
17. Water is used as a coolant in automobiles radiators because it has high specific heat capacity. So, it absorbs a large amount of heat for a degree rise in temperature.
18. The magnitude of upthrust on a body due to a liquid depends on: Volume of the body submerged in the liquid . Density of the liquid in which the body is submerged.
19. The force of attraction is equal to the weight of the object. So, an apple weighing 1N attracts the Earth with 1N force.
20. The center of gravity of an object is the point one can use as the place where gravity pulls on the object.