HOME WORK - 04/10/2019 - PHYSICS - NIOS,CBSE,BBOSE,STATE BOARD - QUESTIONS BANK - 57Q

Q1. Discuss the nature of laws of physics.

Q2. How has the application of the laws of physics led to better quality of life?

Q3. What is meant by significant figures in measurement?

Q4. Find the number of significant figures in the following quantity, quoting the
relevant laws: (i) 426.69 (ii) 4200304.002 (iii) 0.3040 (iv) 4050 m (v) 5000

Q5. The length of an object is 3.486 m, if it is expressed in centimetre (i.e. 348.6 cm) will there be any change in number of significant figures in the two cases.

Q6. What are the four applications of the principles of dimensions? On what principle are the above based?

Q7. The mass of the sun is 2 × 1030 kg. The mass of a proton is 2 × 10–27 kg. If the sun was made only of protons, calculate the number of protons in the sun?

Q8. Earlier the wavelength of light was expressed in angstroms. One angstrom equals 10–8 cm. Now the wavelength is expressed in nanometers. How many
angstroms make one nanometre?

Q9. A radio station operates at a frequency of 1370 kHz. Express this frequency in GHz.

Q10. How many decimetres are there in a decametre? How many MW are there in one GW?

Q11. Experiments with a simple pendulum show that its time period depends on its length (l) and the acceleration due to gravity (g). Use dimensional analysis to obtain the dependence of the time period on l and g.

Q12. Consider a particle moving in a circular orbit of radius r with velocity v and acceleration a towards the centre of the orbit. Using dimensional analysis, show that a ∝ v2/r.

Q13. You are given an equation: mv = Ft, where m is mass, v is speed, F is force and t is time. Check the equation for dimensional correctness

Q14. Make diagrams to show how to find the following vectors: (a) B – A, (b) A + 2B, (c) A – 2B and (d) B – 2A.

Q15. Two vectors A and B of magnitudes 10 units and 12 units are anti-parallel. Determine A + B and A – B.

Q16. Two vectors A and B of magnitudes A = 30 units and B = 60 units respectively are inclined to each other at angle of 60 degrees. Find the resultant vector.

17. Suppose vector A is parallel to vector B. What is their vector product? What will be the vector product if B is anti-parallel to A?

18. Suppose we have a vector A and a vector C = 12 B. How is the direction of vector A × B related to the direction of vector A × C.

19. Suppose vectors A and B are rotated in the plane which contains them. What happens to the direction of vector C = A × B.

20. Suppose you were free to rotate vectors A and B through arbitrary amounts keeping them confined to the same plane. Can you make vector C = A × B to
point in exactly opposite direction?

21. If vector A is along the x-axis and vector B is along the y-axis, what is the direction of vector C = A × B? What happens to C if A is along the y-axis and
B is along the x-axis?

22. A and B are two mutually perpendicular vectors. Calculate (a) A . B and (b) A × B.

23. A vector A makes an angle of 60 degrees with the x-axis of the xy-system of coordinates. If its magnitude is 50 units, find its components in x, y directions.If another vector B of the same magnitude makes an angle of 30 degrees with the X-axis of the XY- system of coordinates. Find its components now. Are
they same as before?

24. A unit used for measuring very large distances is called a light year. It is the distance covered by light in one year. Express light year in metres. Take
speed of light as 3 × 108m s–1.

25. Meteors are small pieces of rock which enter the earth’s atmosphere occasionally at very high speeds. Because of friction caused by the
atmosphere, they become very hot and emit radiations for a very short time before they get completely burnt. The streak of light that is seen as a result is called a ‘shooting star’. The speed of a meteor is 51 km s–1 In comparison, speed of sound in air at about 200 C is 340 m s–1 Find the ratio of magnitudes of the two speeds.

26. The distance covered by a particle in time t while starting with the initial velocity u and moving with a uniform acceleration a is given by s = ut + (1/2)at2. Check the correctness of the expression using dimensional analysis.

27. Newton’s law of gravitation states that the magnitude of force between two particles of mass m1 and m2 separated by a distance r, where G is the universal constant of gravitation. Find the dimensions of G.

28. Hamida is pushing a table in a certain direction with a force of magnitude 10N. At the same time her, classmate Lila is pushing the same table with a
force of magnitude 8 N in a direction making an angle of 60 Degree to the direction in which Hamida is pushing. Calculate the magnitude of the resultant force
on the table and its direction.

29. A physical quantity is obtained as a dot product of two vector quantities. Is it a scalar or a vector? What is the nature of a physical quantity obtained as
cross product of two vectors?

30. John wants to pull a cart applying a force parallel to the ground. His friend Ramu suggests that it would be easier to pull the cart by applying a force at
an angle of 30 degrees to the ground. Who is correct and why?

31.Two vectors are given by 5 ˆ i – 3 ˆ j and 3 ˆ i – 5 ˆ j . Calculate their scalar and vector products.

32. Is it possible for a moving body to have non-zero average speed but zero average velocity during any given interval of time? If so, explain.

33. A lady drove to the market at a speed of 8 km h–1. Finding market closed, she came back home at a speed of 10 km h–1. If the market is 2km away from her
home, calculate the average velocity and average speed.

34. Can a moving body have zero relative velocity with respect to another body? Give an example.

35. A person strolls inside a train with a velocity of 1.0 m s–1 in the direction of motion of the train. If the train is moving with a velocity of 3.0 m s–1, calculate
his (a) velocity as seen by passengers in the compartment, and (b) velocity with respect to a person sitting on the platform.

36. A stone is dropped from a height of 50m and it falls freely. Calculate the (i) distance travelled in 2 s, (ii) velocity of the stone when it reaches the ground, and (iii) velocity at 3 s i.e., 3 s after the start.

37. A motorcyclist moves along a straight road with a constant acceleration of 4m s–2. If initially she was at a position of 5m and had a velocity of
3m s–1, calculate
(i) the position and velocity at time t = 2s, and
(ii) the position of the motorcyclist when its velocity is 5ms–1.

38. A car A is travelling on a straight road with a uniform speed of 60km h–1. Car B is following it with uniform velocity of 70 km h–1. When the distance
between them is 2.5 km, the car B is given a decceleration of 20 km h–1. At what distance and time will the car B catch up with car A?

39. A car starting from rest has an acceleration of 10ms–2. How fast will it be going after 5s?

40. A body starting from rest covers a distance of 40 m in 4s with constant acceleration along a straight line. Compute its final velocity and the time
required to cover half of the total distance.

41. A car moves along a straight road with constant aceleration of 5 ms–2. Initially at 5m, its velocity was 3 ms–1 Compute its position and velocity at t = 2 s.

42. With what velocity should a body be thrown vertically upward so that it reaches a height of 25 m? For how long will it be in the air?

43. A ball is thrown upward in the air. Is its acceleration greater while it is being thrown or after it is thrown?

44. Distinguish between average speed and average velocity.

45. A car C moving with a speed of 65 km h–1 on a straight road is ahead of motorcycle M moving with the speed of 80 km h–1 in the same direction.
What is the velocity of M relative to A?

46. How long does a car take to travel 30m, if it accelerates from rest at a rate of 43.0 m/s2?

47. A motorcyclist covers half of the distance between two places at a speed of 30 km h–1 and the second half at the speed of 60 kmh–1. Compute the average
speed of the motorcycle.

48. A duck, flying directly south for the winter, flies with a constant velocity of 20 km h–1 to a distance of 25 km. How long does it take for the duck to fly
this distance?

49. Bangalore is 1200km from New Delhi by air (straight line distance) and 1500 km by train. If it takes 2h by air and 20h by train, calculate the ratio of the
average speeds.

50. A car accelerates along a straight road from rest to 50 kmh–1 in 5.0 s. What is the magnitude of its average acceleration?

51. A body with an initial velocity of 2.0 ms–1 is accelerated at 8.0 ms–2 for 3 seconds. (i) How far does the body travel during the period of acceleration?
(ii) How far would the body travel if it were initially at rest?

52. A ball is released from rest from the top of a cliff. Taking the top of the cliff as the reference (zero) level and upwards as the positive direction, draw (i) the
displacement-time graph, (ii) distance-time graph (iii) velocity-time graph, (iv) speed-time graph.

53. A ball thrown vertically upwards with a velocity v0 from the top of the cliff of height h, falls to the beach below. Taking beach as the reference (zero) level,
upward as the positive direction, draw the motion graphs. i.e., the graphs between (i) distance-time, (ii) velocity-time, (iii) displacement-time, (iv) speed - time graphs.

54. A body is thrown vertically upward, with a velocity of 10m/s. What will be the value of the velocity and acceleration of the body at the highest point?

55. Two objects of different masses, one of 10g and other of 100g are dropped from the same height. Will they reach the ground at the same time? Explain
your answer.

56. What happens to the uniform motion of a body when it is given an acceleration at right angle to its motion?

57. What does the slope of velocity-time graph at any instant represent?