Motion and Time - Class 7 - Science
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Back Questions - Motion and Time | NCERT | Science | Class 7
Classify the following as motion along a straight line, circular or oscillatory motion:
(i) Motion of your hands while running.
(ii) Motion of a horse pulling a cart on a straight road.
(iii) Motion of a child in a merry-go-round.
(iv) Motion of a child on a see-saw.
(v) Motion of the hammer of an electric bell.
(vi) Motion of a train on a straight bridge.
(i) Motion of your hands while running.
The movement of the hands while running is back and forth in a regular repetitive manner. This type of motion is typically along a curved path but does demonstrate a repetitive to-and-fro motion which is similar to an oscillatory motion.
(ii) Motion of a horse pulling a cart on a straight road.
This example describes motion along a straight and defined path, without deviation from its straight-line trajectory. This is motion along a straight line.
(iii) Motion of a child in a merry-go-round.
A merry-go-round moves in a circle at a constant radius from the center of the apparatus. Thus, this is an example of circular motion.
(iv) Motion of a child on a see-saw.
A see-saw moves up and down around a fixed pivot point in a regular and repeating manner. This is an example of oscillatory motion, as it involves a repetitive swinging motion about a fixed point.
(v) Motion of the hammer of an electric bell.
The hammer of an electric bell moves back and forth rapidly, striking the bell to produce sound. This is a repetitive to-and-fro movement around a fixed axis, classified as oscillatory motion.
(vi) Motion of a train on a straight bridge.
Similar to the horse pulling a cart, the motion of a train on a straight bridge involves movement along a direct and straight line. This too is an example of motion along a straight line.
Which of the following are not correct?
(i) The basic unit of time is second.
(ii) Every object moves with a constant speed.
(iii) Distances between two cities are measured in kilometres.
(iv) The time period of a given pendulum is constant.
(v) The speed of a train is expressed in $\mathrm{m} / \mathrm{h}$.
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Sign up nowA simple pendulum takes $32 \mathrm{~s}$ to complete 20 oscillations. What is the time period of the pendulum?
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Sign up nowThe distance between two stations is $240 \mathrm{~km}$. A train takes 4 hours to cover this distance. Calculate the speed of the train.
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Sign up nowThe odometer of a car reads $57321.0 \mathrm{~km}$ when the clock shows the time 08:30 AM. What is the distance moved by the car, if at 08:50 AM, the odometer reading has changed to $57336.0 \mathrm{~km}$ ? Calculate the speed of the car in $\mathrm{km} / \mathrm{min}$ during this time. Express the speed in $\mathrm{km} / \mathrm{h}$ also.
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Sign up nowSalma takes 15 minutes from her house to reach her school on a bicycle. If the bicycle has a speed of $2 \mathrm{~m} / \mathrm{s}$, calculate the distance between her house and the school.
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Sign up nowShow the shape of the distance-time graph for the motion in the following cases:
(i) A car moving with a constant speed.
(ii) A car parked on a side road.
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Sign up nowWhich of the following relations is correct?
(i) Speed $=$ Distance $\times$ Time
(ii) $\quad$ Speed $=\frac{\text { Distance }}{\text { Time }}$
(iii) $\quad$ Speed $=\frac{\text { Time }}{\text { Distance }}$
(iv) $\quad$ Speed $=\frac{1}{\text { Distance } \times \text { Time }}$
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Sign up nowThe basic unit of speed is:
(i) $\mathrm{km} / \mathrm{min}$
(ii) $\mathrm{m} / \mathrm{min}$
(iii) $\mathrm{km} / \mathrm{h}$
(iv) $\mathrm{m} / \mathrm{s}$
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Sign up nowA car moves with a speed of $40 \mathrm{~km} / \mathrm{h}$ for 15 minutes and then with a speed of $60 \mathrm{~km} / \mathrm{h}$ for the next 15 minutes. The total distance covered by the car is:
(i) $100 \mathrm{~km}$
(ii) $25 \mathrm{~km}$
(iii) $15 \mathrm{~km}$
(iv) $10 \mathrm{~km}$
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Sign up nowSuppose the two photographs, shown in Fig. 9.1 and Fig. 9.2, had been taken at an interval of 10 seconds. If a distance of 100 metres is shown by $1 \mathrm{~cm}$ in these photographs, calculate the speed of the fastest car.
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Sign up nowFig. 9.15 shows the distance-time graph for the motion of two vehicles A and B. Which one of them is moving faster?
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Sign up nowWhich of the following distance-time graphs shows a truck moving with speed which is not constant?
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Sign up nowExtra Questions - Motion and Time | NCERT | Science | Class 7
93: The time taken by Rohan in five different races to run a distance of 500 m was 3.20 minutes, 3.37 minutes, 3.29 minutes, 3.17 minutes, and 3.32 minutes. Find the average times taken by him in the races.
To calculate the average time taken by Rohan in the races, we first need to find the total time he spent running in all five races, which can be computed as follows:
$$ \text{Total time} = 3.20 + 3.37 + 3.29 + 3.17 + 3.32 = 16.35 \text{ minutes} $$
Next, to find the average, we divide this total time by the number of races:
$$ \text{Average time} = \frac{\text{Total time}}{\text{Number of races}} = \frac{16.35}{5} $$
Calculating this gives:
$$ \text{Average time} = \frac{16.35}{5} = 3.27 \text{ minutes} $$
Thus, the average time taken by Rohan in the races is 3.27 minutes.
From the foot of a tower 90 m high, a stone is thrown up so as to reach the top of the tower with zero velocity. Two seconds later another stone is dropped from the top of the tower. Find when will the two stones meet for the first time?
(A) 4.5 s
(B) 1.7 s
(C) 3.1 s
(D) 2.8 s
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Sign up nowSusan is 15 minutes late for a meeting she was supposed to attend at 2:45 p.m. So, she reached the meeting hall at:
A) 2:30 p.m. B) 2:45 p.m. C) 3:00 p.m. D) 3:15 p.m. E) 3:00 a.m.
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