Question:
Define buoyant force.What is its unit ?
Answer:
The upward force acting on an object immersed in a fluid is called buoyant force.Its unit is the same as that of force, i.e.,newton (N).
Motion
Q 1.
The equation S = ut + ½at2 gives information as
(a) velocity is a function of time.
(b) velocity is a function of position.
(c) Position is a function of time.
(d) Position is function of velocity and time.
Q 2.
Fill in the blanks :
The rate of change of velocity of a moving body with time is called ______.
Q 3.
Are motion and rest absolute or relative? Explain with an example.
Q 4.
What do you mean by a body in rest?
Q 5.
Which of the following is true for displacement?
(a) It cannot be zero.
(b) Its magnitude is greater than the distance travelled by the object.
Q 6.
Under what condition(s) is the magnitude of average velocity of an object equal to its average speed?
Q 7.
Fig (below) shows the distance-time graph of three objects A,B and C. Study the graph and answer the following questions:
(a) Which of the three is travelling the fastest?
(b) Are all three ever at the same point on the road?
(c) How far has C travelled when B passes A?
(d) How far has B travelled by the time it passes C?
Q 8.
A bus decreases its speed from 80 km/h to 60 km/h in 5 s. Find the acceleration of the bus.
Q 9.
A racing car has a uniform acceleration of 4 m s–2.
What distance will it cover in 10 s after start?
Q 10.
What is the average velocity over the “round trip” of an object that is thrown straight up from the ground and falls straight back down to the ground?
Q 11.
Which of the following is true for displacement ?
(a) It cannot be zero.
(b) Its magnitude is greater than the distance travelled by the object.
Q 12.
Calculate the mass of air enclosed in a room of length,breadth and height equal to 5 m, 3 m and 4 m respectively.Density of air =
.
Q 13.
Why do objects float or sink when placed on the surface of a liquid ?
Q 14.
When will you say a body is in (i) uniform acceleration? (ii) nonuniform acceleration?
Q 15.
Distinguish between speed and velocity.
Q 16.
A trolley, while going down an inclined plane, has an acceleration of
starting from rest.What will be its velocity 3 s after the start ?
Q 17.
Is displacement a scalar quantity ?
Q 18.
Derive graphically the equation v=u + at,where the symbols have their usual meanings.
Q 19.
Using velocity time graph,establish the relation s = ut +
,where the symbols have their usual meanings.
Q 20.
Rohan and his sister Saniya go to school together in their car.Rohan drives much faster than Saniya.Saniya tells Rohan not to take the risk of over speeding.She tells him that time taken to reach the school would depend upon average speed.By overspeeding for a little while,the risk involved is much greater compared to the little time saved. Answer the following questions based on the above paragraph.
(i) Which values are displayed by Saniya?
(ii) Is Saniya right in her statement?
(iii) How do you define average speed?
Q 21.
A Physics teacher explains the concept of relative velocity to her students in class. She emphasises that when two bodies are moving in opposite directions, their relative velocity is sum of the velocities of the two. And when two bodies are moving in the same direction, their relative velocity is difference of the velocities of the two. Students are confused. The teacher then takes two balls one red and the other green. She says suppose red ball moves with a velocity of 5 m/s and green ball moves with a velocity of 4 m/s from a common point, and along the same straight line. If red ball is moving to the right and green ball is moving to the left, then after 1 sec, red ball is at R', where RR' = 5 m and green ball is at G' where GG' = 4 m, In Fig.(a).The distance between the two balls after 1 sec = G' R' = GG' + RR' = (4 + 5) = 9 m.
This is the magnitude of their relative velocity. If both the balls are moving to the right, as shown in Fig. (b), the distance between the two balls after 1 sec. = G' R' = RR' - GG' = 5 - 4 = 1 m.Read the above passage and answer the following questions :
(i) What value has the Physics teacher displayed ?
(ii) What have the students picked up?
(iii) Give at least one practical example of the concept.
Q 22.
A Physics teacher is explaining the difference between average speed and average velocity to her students.
She emphasises that average speed is more relevant than average velocity,because displacement from one place to other is only theoretical, being the shortest distance between two places. Average speed is the real entity that matters,taking into account the actual time taken to travel the actual distance between the two stations.
Read the above passage and answer the following questions :
(i) Do you agree with the statement of Physics teacher?
(ii) The shortest distance between Ambala and Delhi is 200 km.A train takes 4 hrs and covers a distance of 210 km in going from Ambala to Delhi via Karnal.Another train takes 5 hrs and covers 250 km distance in going from Ambala to Delhi via Saharanpur.What is the average speed of these two trains ? What would be the average velocity of a train that takes 2.5 hrs to cover 200 km distance ?
(iii) What values do you learn from this discussion ?
Q 23.
A metallic sphere of radius 2.0 cm is completely dipped in water.Find the force of buoyancy on it.
Q 24.
What do you mean by buoyancy ?
Q 25.
Explain the reason due to which buoyancy arises.
Q 26.
What is Archimedes’ Principle ? How can it be experimentally verified ?
Q 27.
When a plastic block is released under water,it never stays under water but instead comes to the surface of water.Explain why ?
Q 28.
A farmer moves along the boundary of a square field of side 10 m in 40 s. What will be the magnitude of displacement of the farmer at the end of 2 minutes 20 seconds?
Q 29.
A ship is moving at a speed of 56 km/h.One second later,it is moving at 58 km/h.What is its acceleration ?
Q 30.
in Fig, shows the distance-time graph of three objects A, B and C. Study the graph and answer the following questions :
(a) Which of the three is travelling the fastest ?
(b)Are ail three ever at the same point on the road ?
(c) How far has C travelled when B passes A ?
(d) How far has B travelled by the time it passes C ?
Q 31.
What is the SI unit of displacement ?
Q 32.
Can displacement be negative ?
Q 33.
In addition to speed,what else should be known to predict the position of a moving body from a given starting point ?
Q 34.
What remains constant in uniform circular motion ?
Q 35.
What changes continuously in uniform circular motion ?
Q 36.
What conclusion do you draw when displacement-time graph of a body is as shown in Fig.?
Q 37.
Define speed and velocity.What are their SI units ?
Q 38.
Use graphical method to derive the relation
-
= 2 as,where the symbols have their usual meanings.
Q 39.
Draw distance-time graph for a body (i) at rest (ii) in uniform motion (iii) in non-uniform motion.Discuss their interpretation.
Q 40.
Derive graphically the equation of motion for position-velocity relation of a body moving with uniform acceleration.
Q 41.
Puja and Neha are close friends.Puja is a science graduate and Neha is a commerce graduate.Puja finds that while driving on a clear highway,Neha often exceeds the speed limit and agrues that there is no harm in doing so when the road is clear.Puja does not agree with her and tells her that with increase in speed, stopping distance of car would increase and she would not be able to manage things if some stray cattle etc. appears suddenly on the way.Read the above passage and answer the following questions :
(i) Is Puja right in her statement?
(ii) What values are displayed by Puja in her statement?
(iii) How is stopping distance related to speed of vehicle?
Q 42.
A nail is driven into a wooden board by using a hammer.The impact of the hammer on the head of the nail produces a thrust of 25 N.If the area of the head is
and of the tip
,find the pressures on the head and the tip of the tail.
Q 43.
Calculate the mass of a body whose volume is
and relative density is 0.52.
Q 44.
A body of 2.0 kg floats in a liquid.What is the buoyant force on the body ?
Q 45.
Calculate the pressure when a force of 200 N acts on an
Q 46.
What force acting on an area of
will produce a pressure of 500 Pa ?
Q 47.
Define density.Give its unit
Q 48.
What is relative density ? What is its unit ?
Q 49.
State one important effect produced by the buoyant force exerted by water.
Q 50.
Why do you feel lighter when you swim ?
