Question:
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 ?
Answer:
(i) Yes, we agree with the statement of Physics teacher.
(ii) Average speed of first train = ==52.5 km/hr.
Average speed of second train ===80 km/hr.
(iii) From the above discussion, we learn that if two places,say A and B between which we have to travel are connected by different routes, we should choose the route in which we have to travel the minimum distance ; and along which road conditions are good. This would save us time and also the cost of travel. We can advise our friends accordingly and fulfil our social obligations.
Motion
Q 1.
Derive graphically the equation of motion for position-velocity relation of a body moving with uniform acceleration.
Q 2.
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 3.
A particle moves over three quarters of a circle of radius r.What is the magnitude of its displacement ?
Q 4.
The mass of an empty 40 litre petrol tank of a vehicle is 8.0 kg.What will be its mass when filled completely with a fuel of density 700
Q 5.
What is represented by the graphs in Fig.?
.
Q 6.
A cyclist cycles for t second at a speed of 3 m/s and then for the same time at a speed of 5 m/s along a straight road due north. What is the average speed of the cyclist?
Q 7.
Write the three equations of uniformly accelerated motion. Give the meaning of each symbol in them.
Q 8.
Calculate the greatest and the least pressure exerted by a metal block of size 20 cm x 8 cm x 5 cm and having a mass of 5 kg.
Q 9.
Name the quantity that represents rate of change of velocity ?
Q 10.
A body starts from rest.What is zero ?
Q 11.
Why is a slight blow on a cork of bottle fully filled with a liquid sufficient to break the bottle ?
Q 12.
When will you say a body is in (i) uniform acceleration? (ii) nonuniform acceleration?
Q 13.
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 14.
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 15.
A particle moves along the x axis from A to B. Which Of the following values of the initial and final coordinates, which results in a negative displacement?
(a) A = 4m, B = 6m
(b) A = −4m, B = −2m
(c) A = −4m, B = −8m
(d) A = −4m, B = 2m
Q 16.
What will be the initial velocity of an object under free fall?
Q 17.
Air is a fluid and our bodies displace air.As a result of this,a buoyant force is acting on each one of us.
(a)What is the approximate density of your body ?
(b) What is your approximate volume ?
(c) Estimate the magnitude of the buoyant force on you due to the air displaced.Consider your mass to be 75 kg.
(d)Does it mean that your weight is more than the scale reading ?
(Given density of air,pa =
)
Q 18.
Under what conditions(s) is the magnitude of average
Q 19.
What conclusion do you draw when displacement-time graph of a body is as shown in Fig.?
Q 20.
What is the relationship between the buoyant force on an object and the liquid displaced by it ?
Q 21.
What is pressure in case of fluids ? What is Pascal’s law ?
Q 22.
Why does a person feel pain when he stands on a pile of gravel than when he stands on a bed of sand ?
Q 23.
A body thrown vertically upwards reaches a maximum height h.It then returns to ground.Calculate the distance travelled and the displacement.
Q 24.
What can you say about the motion of an object whose distance-time graph is a straight line parallel to the time axis ?
Q 25.
The speed-time graph for a car is shown is Fig.
(a) Find how far does the car travel in the first 4 seconds.Shade the area on the graph that represents the distance travelled by the car during this period.
(b) Which part of the graph represents uniform motion of the car ?
.
Q 26.
Draw speed-time graph for a body (i) at rest (ii) in uniform motion (iii) in uniformly accelerated motion.Discuss the results briefly.
Q 27.
A force of 16 N is distributed uniformly on one surface of a cube of edge 8 cm.Find the pressure on this surface.
Q 28.
An artificial satellite is moving in a circular orbit of radius 42250 km. Calculate its speed if it takes 24 hours to revolve around the Earth.
Q 29.
The mass of a solid rectangular block of iron is 23.6 g and its dimensions are 2.1 cm x 1.2 cm x 1.1 cm.Calculate the density of iron.
Q 30.
What is the relation between true weight,apparent weight and the loss in weight of a body immersed in a fluid ? Give some practical applications of Archimedes’Principle.
Q 31.
Pascal’s law states that a fluid in a confined space expands into every possible space if it is put under pressure.This law plays a very important role in our lives.Give three applications with brief description.
Q 32.
A car travels along a straight line for first half time with speed 40 km/h and the second half time with speed 60 km/h. Find the average speed of the car.
Q 33.
A body starts to slide over a horizontal surface with an initial velocity of 0-5 m/s. Due to friction, its velocity decreases at the rate of 0.05
.How much time will it take for the body to stop ?
Q 34.
When will you say a body is in (») uniform acceleration ? (ii) non-uniform acceleration ?
Q 35.
Explain the terms : uniform motion and non-uniform motion with examples.
Q 36.
Relative density of silver is 10.8.The density of water is
.What is the density of silver in SI units ?
Q 37.
An electric train is moving with a velocity of 120 km/h. How much distance will it move in 30 s ?
Q 38.
What is SI unit of speed ? Is it same for velocity ?
Q 39.
What is the acceleration of a body moving with uniform velocity ?
Q 40.
If velocity-time graph of a body is as shown in Fig.,what is the nature of motion ?
Q 41.
A weather forecasting plastic balloon of volume
contains hydrogen of density
.The mass of the empty balloon is 7.15 kg.Calcuiate (a) the mass or 'hydrogen in the balloon (b) Tne mass of balloon filled with hydrogen.
Q 42.
The density of turpentine oil is
.What will be its relative density ?
Q 43.
Why are sleepers used below the rails ?
Q 44.
A scalar quantity has ?
(a) magnitude only
(b) direction only
(c) both direction and magnitude
(d) none of these
Q 45.
A particle is moving in a circle of diameter 5 m. Calculate the distance covered and the displacement when it completes 3 revolutions.
Q 46.
Is displacement a scalar quantity ?
Q 47.
What type of motion is the motion of tip of second’s hand of a watch ? Is it uniform or accelerated ?
Q 48.
Using velocity time graph,establish the relation s = ut +
,where the symbols have their usual meanings.
Q 49.
Use graphical method to derive the relation
-
= 2 as,where the symbols have their usual meanings.
Q 50.
A force of 100 N is applied on an object of area
.Calculate the pressure.
