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Physics 1 Marks Question

Rest and Motion: Kinematics · Rajasthan Board (RBSE) STD 12 Science (Rajasthan - English Medium). 12 questions.

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Question 11 Mark
A particle starts from a point A and travels along the solid curve shown in figure. Find approximately the position B of the particle such that the average velocity between the positions A and B has the same direction as the instantaneous velocity at B.
Answer
At position B instantaneous velocity has direction along $\overrightarrow{\text{BC}}.$ For average velocity between A and B.$\text{V}_{\text{ave}}=\frac{\text{displacement}}{\text{times}}=\Big(\frac{\overrightarrow{\text{AB}}}{\text{t}}\Big)$
t = time We can see that $\overrightarrow{\text{AB}}$ is along $\overrightarrow{\text{BC}}$ i.e. they are in same direction. The point is B(5m, 3m).
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Question 21 Mark
An $\text{NCC}$ parade is going at a uniform speed of $6\ km/ h$ through a place under a berry tree on which a bird is sitting at a height of $12.1m.$ At a particular instant the bird drops a berry. Which cadet $($give the distance from the tree at the instant$)$ will receive the berry on his uniform?
Answer
Let the true of fall be $‘t\ ’$ initial velocity $u = 0$ Acceleration $a = 9.8m/s^2$
Distance $\text{S}=\frac{12}{1}\text{m}$
$\therefore\text{S = ut}+\frac{1}{2}\text{at}^2$
$\Rightarrow12.1=0+\frac{1}{2}(9.8)\times\text{t}^2$
$\Rightarrow\text{t}^2=\frac{12.1}{4.9}=2.46$
$\Rightarrow\text{t}=1.57\text{ sec}$
For cadet velocity $= 6\ km/ hr = 1.66m/sec$
Distance $= vt = 1.57 \times 1.66 = 2.6m.$
The cadet, $2.6m$ away from tree will receive the berry on his uniform.
 
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Question 31 Mark
An object having a velocity $4.0\ m/s$ is accelerated at the rate of $1.2\ m/s^2$ for $5.0s.$ Find the distance travelled during the period of acceleration.
Answer
$u = 4\ m/s, a = 1.2\ m/s^2, t = 5$ sec Distance
$=\text{s}=\text{ut}+\frac{1}2{}\text{at}^2$
$=4(5)+\frac{1}{2}(1.2)5^2$
$=35\text{m}.$
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Question 41 Mark
A person travelling at $43.2\ km/h$ applies the brake giving a deceleration of $6.0\ m/s^2$ to his scooter. How far will it travel before stopping?
Answer
Initial velocity $u = 43.2\ km/hr = 12m/s$
$u = 12m/s, v = 0$
$a = -6m/s^2 ($deceleration$)$
Distance $\text{s}=\frac{\text{v}^2-\text{u}^2}{2(-6)}=12\text{m}$
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Question 51 Mark
Figure shows the graph of the $x-$coordinate of a particle going along the $X-$axis as a function of time. Find:
  1. The average velocity during $0$ to $10s.$
  2. Instantaneous velocity at $2, 5, 8$ and $12s.$
Answer
  1. Displacement in $0$ to $10 \sec$ is $1000m.$
time $= 10 \sec.$
$\text{V}_{\text{ave}}=\frac{\text{s}}{\text{t}}=\frac{100}{10}=10\text{m/s}.$
  1. At $2 \sec$ it is moving with uniform velocity $\frac{50}{2.5}=20\text{m/s}.$
at $2 \sec. V_{inst} = 20m/s.$
At $5 \sec$ it is at rest.
$V_{inst} =$ zero.
At $8 \sec$ it is moving with uniform velocity $20m/s$
$V_{inst} = 20m/s$
At $12 \sec$ velocity is negative as it move towards initial position. Vinst $= -20m/s.$
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Question 61 Mark
The increase in the speed of a car is proportional to the additional petrol put into the engine. Is it possible to accelerate a car without putting more petrol or less petrol into the engine?
Answer
Move in circular path with constant speed.
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Question 71 Mark
Galileo was punished by the Church for teaching that the sun is stationary and the earth moves around it. His opponents held the view that the earth is stationary and the sun moves around it. If the absolute motion has no meaning, are the two, viewpoints not equally correct or equally wrong?
Answer
Yes, from relative motion we can this.
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Question 81 Mark
A car travels at a speed of 60km/hr due north and the other at a speed of 60km/hr due east. Are the velocities equal? If no, which one is greater? If you find any of the questions irrelevant, explain.
Answer
There are equal because they have different directions. There magnitude can be compared.
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Question 101 Mark
When a particle moves with constant velocity, its average velocity, its instantaneous velocity and its speed are all equal. Comment on this statement.
Answer
Its average velocity and instantaneous velocity will be equal but we cannot compare these with average speed as one is vector and other is scalar.
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Question 111 Mark
The velocity of a particle is towards west at an instant. Its acceleration is not towards west, not towards east, not towards north and not towards south. Give an example of this type of motion.
Answer
Projectile at highest point because at the highest point vertical velocity become zero.
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Question 121 Mark
Two particles A and B start from rest and move for equal time on a straight line. The particle A has an acceleration a for the first half of the total time and 2a for the second half. The particle B has an acceleration 2a for the first half and a for the second half. Which particle has covered larger distance?
Answer
Second particle

Area under (v, t) graph gives displacement. For graph (2) area is more.
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