Question:
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?
Answer:
(a) Object B is travelling the fastest. We can determine it in two ways. Slope of the distance-time line represents the speed of the object. In this case, object B has the highest slope.
(Note: slope is also represented by the angle subtended by the distance-time line with x-axis. Steeper the angle, higher the speed.)
(b) No all objects never meet at the same point.
(c) When B and A meets at point m, the Object C is at n, which is approximately 8km on distance axis.
(d) B meets C at point k. The position on distance-axis is 9 units away from origin O. One unit on distance-axis = 4/7 (7 units = 4km). ∴ Object B is = 9 x 4/7 = 5.14 km.
Motion
Q 1.
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 2.
Derive graphically the equation of motion for position-velocity relation of a body moving with uniform acceleration.
Q 3.
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 4.
The density of turpentine oil is
.What will be its relative density ?
Q 5.
Are motion and rest absolute or relative? Explain with an example.
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.
Mathematically prove that the distance (S) travelled by an object is the average mean of initial velocity(u) and final velocity(v) having constant acceleration(a) in the direction of motion in a straight line.
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.
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 10.
A particle is moving in a circle of diameter 5 m. Calculate the distance covered and the displacement when it completes 3 revolutions.
Q 11.
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 12.
Define thrust What is its unit ?
Q 13.
Distinguish between speed and velocity.
Q 14.
If velocity-time graph of a body is as shown in Fig.,what is the nature of motion ?
Q 15.
What is represented by the graphs in Fig.?
.
Q 16.
An object weighs 9.8 N in air and 9.0 N when fully immersed in water.How much is the buoyant force on the object ?
Q 17.
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 18.
When will you say a body is in (i) uniform acceleration? (ii) nonuniform acceleration?
Q 19.
A train is travelling at a speed of 90 kmh–1. Brakes are applied so as to produce a uniform acceleration of – 0.5 ms–2. Find how far the train will go before it is brought to rest.
Q 20.
Fill in the blanks :
If the position of an object does not change with time, it is said to be at _____.
Q 21.
Use graphical method to derive the relation
-
= 2 as,where the symbols have their usual meanings.
Q 22.
Draw distance-time graph for a body (i) at rest (ii) in uniform motion (iii) in non-uniform motion.Discuss their interpretation.
Q 23.
A cube of edge length 10 cm is placed inside a liquid.The pressure at the centre of the face is 15 Pa.Find the force exerted by the liquid on this face.
Q 24.
Why is a slight blow on a cork of bottle fully filled with a liquid sufficient to break the bottle ?
Q 25.
Fill in the blanks :
The rate of change of velocity of a moving body with time is called ______.
Q 26.
A body thrown vertically upwards reaches a maximum height h.It then returns to ground.Calculate the distance travelled and the displacement.
Q 27.
A train starting from rest moves with a uniform acceleration of 0.2
for 5 minutes.Calcualte the speed acquired and the distance travelled in this time.
Q 28.
Under what conditions(s) is the magnitude of average
Q 29.
A racing car has a uniform acceleration of 4
.What distance will it cover in 10 s after start ?
Q 30.
Can distance be negative ?
Q 31.
What remains constant in uniform circular motion ?
Q 32.
What can you calculate from speed-time graph of a body ?
Q 33.
Explain the terms : uniform motion and non-uniform motion with examples.
Q 34.
State velocity-time relation in uniformly accelerated motion. Use graphical method to obtain this relation.
Q 35.
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 36.
A metallic sphere of radius 2.0 cm is completely dipped in water.Find the force of buoyancy on it.
Q 37.
Why does a person feel pain when he stands on a pile of gravel than when he stands on a bed of sand ?
Q 38.
What does the path of an object look like when it is in uniform motion?
Q 39.
What does the slope of distance-time graph indicate?
Q 40.
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 41.
The displacement of a moving object in a given interval of time is zero.Would the distance travelled by the object also be zero ?Justify your answer.
Q 42.
Can displacement and distance ever be equal ?
Q 43.
What is SI unit of speed ? Is it same for velocity ?
Q 44.
In addition to speed,what else should be known to predict the position of a moving body from a given starting point ?
Q 45.
Name the terms represented by various symbols in the equation, v = u + at.
Q 46.
Define the term uniform acceleration.Give one example of uniformly accelerated motion.
Q 47.
Derive graphically the equation v=u + at,where the symbols have their usual meanings.
Q 48.
A stone tied to one end of a string is rotated in a circle.Explain what happens when the stone is released.
Q 49.
Using graphical method,derive the equations
v=u+at and s=ut+
where symbols have their usual meanings.
Q 50.
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.
