Page 100
Q.1 Â Â An object has moved through a distance. Can it have zero displacement? If yes, support your answer with an example.
Sol. Â Â Yes, zero displacement is possible if an object has moved through a distance.
Â Â Â Â Â Â Suppose a ball starts moving from point A and it returns back at same point A, then the distance will be equal to 20 meters while displacement will be zero.
Q.2 Â Â 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 from his initial position?
Sol.
Â Â Â Â Â Â Given, side of the square field = 10m
Â Â Â Â Â Â Therefore, perimeter = 10 m x 4 = 40 m
Â Â Â Â Â Â Farmer moves along the boundary in 40s.
Â Â Â Â Â Â Displacement after 2 m 20 s = 2 x 60 s + 20 s = 140 s =?
Â Â Â Â Â Â Since in 40 s farmer moves 40 mTherefore, in 1s distance covered by farmer =Â Â
Â Â Â Â Â Â Therefore, in 140s distance covered by farmer = 1 Ã— 140 m = 140 m
Â Â Â Â Â Â Now, number of rotation to cover 140 along the boundry Â = Â
Â Â Â Â Â Â
Â Â Â Â Â Â Thus after 3.5 round farmer will at point C of the field.
Â Â Â Â Â Â Therefore, DisplacmentÂ
Â Â Â Â Â Â
Â Â Â Â Â Â
Â Â Â Â Â Â
Â Â Â Â Â Â Thus, after 2 minute 20 second the displacement of farmer will be equal toÂ north east from initial position.Â
Q.3 Â Â Which of the following is true for displacement?
Â Â Â Â Â Â (a) It cannot be zero.
Â Â Â Â Â Â (b) Its magnitude is greater than the distance travelled by the object.
Sol.Â Â Â None
Page 102
Q.1 Â Â Distinguish between speed and velocity.
Sol. Â Â Speed has only magnitude while velocity has both magnitude and direction.
Q.2 Â Â Under what condition(s) is the magnitude of average velocity of an object equal to its average speed?
Sol.Â Â Â The magnitude of average velocity of an object will be equal to its average speed in the condition of uniform velocity.
Q.3 Â Â What does the odometer of an automobile measure?
Sol.Â Â Â In automobiles, odometer is used to measure the distance.
Q.4 Â Â What does the path of an object look like when it is in uniform motion?
Sol.Â Â Â In the case of uniform motion the path of an object will look like a straight line.
Q.5 Â Â During an experiment, a signal from a spaceship reached the ground station in five minutes. What was the distance of the spaceship from the ground station? The signal travels at the speed of light, that is, .
Sol. Â Â Â Here we have, speed =Â
Â Â Â Â Â Time = 5 minute =Â second
Â Â Â Â Â We know that, Distance = Speed Ã— Time
Â Â Â Â Â Distance =Â
Page 103
Q.1 Â Â When will you say a body is in
Â Â Â Â Â Â (i) uniform acceleration?
Â Â Â Â Â Â (ii) non-uniform acceleration?
Sol. Â Â (i) A body is said in uniform acceleration when its motion is along a straight line and its velocity changes by equal magnitude in equal interval of time.
Â Â Â Â Â Â (ii) A body is said in non-uniform acceleration when its motion is along a straight line and its velocity changes by unequal magnitude in equal interval of time.
Q.2 Â Â A bus decreases its speed from 80 km/h to 60 km/h in 5 s. Find the acceleration of the bus.
Sol. Â Â Here we have, u = 80 km/h, v = 60km/h, t = 5s
Â Â Â Â Â Â Therefore, acceleration, a = ?
Â Â Â Â Â Â We know that, v = u + at
Â Â Â Â Â Â 60 km/ h = 80km/h + a Ã— 5s
Â Â Â Â Â Â 60km/h â€“ 80km/h = a Ã— 5s
Â Â Â Â Â Â â€“ 20km/h = a Ã— 5s
Â Â Â Â Â Â a =Â
Â Â Â Â Â Â a = â€“ 4km/h/s
Â Â Â Â Â Â Therefore, Acceleration = â€“4 km/h/s or, â€“1.1Â Â Â
Q. 3 Â Â A train starting from a railway station and moving with uniform acceleration attains a speed of 40 km/h in 10 minutes. Find its acceleration.
Sol.Â Â Â Here we have,
Â Â Â Â Â Â Initial velocity, u = 0,
Â Â Â Â Â Â Final velocity, v = 40km/h = 11.11m/s
Â Â Â Â Â Â Time (t) = 10 minute = 60 x 10=600s
Â Â Â Â Â Â Acceleration (a) =?
Â Â Â Â Â Â We know that, v = u + at
Â Â Â Â Â Â 40km/h = 0km/h + a Ã— 10m
Â Â Â Â Â Â 11.11 m/s = a Ã— 600s
Â Â Â Â Â Â a =Â
Page 107
Q.1 Â Â What is the nature of the distance-time graphs for uniform and non-uniform motion of an object?
Sol. Â Â Â (a) The slope of the distance-time graph for an object in uniform motion is straight line.
Â Â Â Â Â Â (b) The slope of the distance-time graph for an object in non-uniform motion is not a straight line.
Q.2 Â Â What can you say about the motion of an object whose distance-time graph is a straight line parallel to the time axis?
Sol. Â Â Â When the slope of distance-time graph is a straight line parallel to time axis, the object is moving with uniform motion.
Q.3 Â Â What can you say about the motion of an object if its speed-time graph is a straight line parallel to the time axis?
Sol. Â Â Â When the slope of a speed time graph is a straight line parallel to the time axis, the object is moving with uniform speed.
Q.4 Â Â What is the quantity which is measured by the area occupied below the velocity-time graph?
Sol. Â Â The quantity of distance is measured by the area occupied below the velocity time graph.
Page 109
Q.1 Â Â A bus starting from rest moves with a uniform acceleration of 0.1 m s^{-2}Â for 2 minutes. Find (a)the speed acquired, (b) the distance travelled.
Sol. Â Â Here we have,
Â Â Â Â Â Â Initial velocity (u) = 0
Â Â Â Â Â Â Acceleration (a) = 0.1ms-2
Â Â Â Â Â Â Time (t) = 2 minute = 120 second
Â Â Â Â Â Â (a) The speed acquired:
Â Â Â Â Â Â We know that, v = u + at
Â Â Â Â Â Â â‡’ v = 0 + 0.1m/s2 x 120 s
Â Â Â Â Â Â â‡’ v = 120 m/s
Â Â Â Â Â Â Thus, the bus will acquire a speed of 120 m/s after 2 minute with the given acceleration.
Â Â Â Â Â Â (b) The distance travelled:
Â Â Â Â Â Â We know that,
Â Â Â Â Â Â
Â Â Â Â Â Â
Â Â Â Â Â Â Thus, bus will tavel a distance of 7200 m or 7.2 km in the given time of 2 minute.Â Â
Page 110
Q.2 Â Â A train is travelling at a speed of 90 km/h. Brakes are applied so as to produce a uniform acceleration of â€“ 0.5 m s^{-2}. Find how far the train will go before it is brought to rest.
Sol. Â Â Here,we have,
Â Â Â Â Â Â Initial velocity, u = 90km/h
Â Â Â Â Â Â
Â Â Â Â Â Â Final velocity, v = 0
Â Â Â Â Â Â Acceleration,a = â€“ 0.5Â
Â Â Â Â Â Â Therefore, distance travelled = ?
Â Â Â Â Â Â We know tha,Â Â
Â Â Â Â Â Â
Â Â Â Â Â Â Â
Â Â Â Â Â Â
Â Â Â Â Â Â Therefore, train will go 625 m be fore it brought to rest.
Q.3 Â Â A trolley, while going down an inclined plane, has an acceleration of 2 cm s^{-2}. What will be its velocity 3 s after the start?
Sol.Â Â Â Here we have,
Â Â Â Â Â Â Initial velocity, u = 0
Â Â Â Â Â Â Acceleration (a) = 2cm/s^{2}Â = 0.02m/s^{2
}Â Â Â Â Â Â Time (t) = 3s
Â Â Â Â Â Â Therefore, Final velocity, v = ?
Â Â Â Â Â Â We know that, v = u + at
Â Â Â Â Â Â Therefore, v = 0 + 0.02Ã— 3s
Â Â Â Â Â Â v = 0.06 m/s
Â Â Â Â Â Â Therefore the final velocity of trolley will be 0.06 m/s after start.Â
Q.4 Â Â A racing car has a uniform acceleration of 4 m s^{-2}. What distance will it cover in 10 s after start?
Sol. Â Â Here we have,
Â Â Â Â Â Â Acceleration, a = 4m/s2
Â Â Â Â Â Â Initial velocity, u = 0
Â Â Â Â Â Â Time, t = 10s
Â Â Â Â Â Â Therefore, Distance (s) covered =?
Â Â Â Â Â Â We know that, Â
Â Â Â Â Â Â
Â Â Â Â Â Â
Â Â Â Â Â Â
Â Â Â Â Â Â Thus, racing car will cover a distance of 200m after start in 10 s with given acceleration.
Q. 5 Â Â A stone is thrown in a vertically upward direction with a velocity of 5 m s^{-1}. If the acceleration of the stone during its motion is 10 m s^{-2}Â in the downward direction, what will be the height attained by the stone and how much time will it take to reach there?
Sol. Â Â Â Here we have,
Â Â Â Â Â Â Initial velocity (u) = 5m/s
Â Â Â Â Â Â Â Final velocity (v) = 0 (Since from where stone starts falling its velocity will become zero)
Â Â Â Â Â Â Acceleration (a) = â€“ 10m/s^{2
}Â Â Â Â Â Â (Since given acceleration is in downward direction, i.e. the velocity of the stone is decreasing, thus acceleration is taken as negative)
Â Â Â Â Â Â Height, i.e. Distance, s =?
Â Â Â Â Â Â Time (t) taken to reach the height =?
Â Â Â Â Â Â We know that,Â
Â Â Â Â Â Â
Â Â Â Â Â Â
Â Â Â Â Â Â
Â Â Â Â Â Â
Â Â Â Â Â Â Now, we know that , v = u + at
Â Â Â Â Â Â
Â Â Â Â Â Â
Â Â Â Â Â Â
Â Â Â Â Â Â Thus, stone will attain a height of 1.25m And time taken to attain the height is 0.5s Â Â
Get 2021 CBSE Crash Course FREE** |
Know How |
sorry but regarding
Q.5 During an experiment, a signal from a spaceship reached the ground station in five minutes. What was the distance of the spaceship from the ground station? The signal travels at the speed of light, that is, 3Ã—108msâˆ’1.
Sol. Here we have, speed = 3Ã—108msâˆ’1
Time = 5 minute = 5Ã—60s=300 second
We know that, Distance = Speed Ã— Time
â‡’ Distance = 3Ã—108msâˆ’1Ã—300s=1800Ã—108m=1.8Ã—1011m
but 3*300=900 or the above please clarify.
Marvellous
Thanks...
You help me a lot...
Excellent
I love this app and very very much thank you
Nice thx to help me
I really can't believe how great this site is. Keep up the good work. I'm going to tell all my friends about this place.
Amazing
Thank you for helping me.
Thank you very very very very much
Your app is very good for me. Thanks
That's really easy to understand
Thanks for help
Thanks for help
it is really very helpfull. it very easy to undrestand. thaks for helping us
Nice app
very nice
Useful
Good
It is very useful thing for me
It's very useful for study
Very nice i understand all the numericals
Very nice i understand all the numericals it is very easy methods
Very good
Very good
It very useful for me
Very understand able and nice answers are there I like this I hope you all are also enjoyed
good
This is too good. I love this
awsome
It was really awesome. At 1st I feel very disturbance by not understanding ncert lessons but this blog let me understand what I not understand and it helped me in my homework and every year I score 2nd toppers but in this year I am sure confidently that I will score toppers in my class as I am from class 9 of bodhisukha school which is in Kathor, badu, barasat. For contact with me-in FB -Abdul kalam 9932573866, WhatsApp no. -8420793786 and my contact number is 8348875067 and 8167600808. Thanks all of you. Please contact me.
nice
I am really impressed with your writing skills as well as with the layout on your weblog. Is this a paid theme or did you customize it yourself? Anyway keep up the nice quality writing, itâ€™s rare to see a nice blog like this one today..
http://wiki.mozillabd.org/index.php?title=User:DaniellaU68