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All questions of Motion in a Plane for NEET Exam

For angles of projection of a projectile (45° – θ) and (45° + θ), the horizontal ranges described by the projectile are in the ratio of [2006]
  • a)
    1: 3
  • b)
    1 : 2
  • c)
    2 : 1
  • d)
    1 : 1
Correct answer is option 'D'. Can you explain this answer?

Arpita Tiwari answered
(45º – θ) & (45º + θ) are complementary angles as 45º – θ + 45º + θ = 90º. We know that if angle of projection of two projectiles make complementary angles, their ranges are equal.
In this case also, the range will be same. So the ratio is 1 : 1.

The cir cular motion of a particle with constant speed is [2005]
  • a)
    periodic but not simple harmonic
  • b)
    simple harmonic but not periodic
  • c)
    periodic and simple harmonic
  • d)
    neither periodic nor simple harmonic
Correct answer is option 'A'. Can you explain this answer?

Rajat Roy answered
In circular motion of a particle with constant speed,  particle repeats its motion after a regular interval of time but does not oscillate about a fixed point. So, motion of particle is periodic but not simple harmonic.

If the angle between the vectors  the value of the product is equal to [2005]
  • a)
    BA2 sinθ
  • b)
    BA2 cosθ
  • c)
    BA2 sinθ cosθ
  • d)
    zero
Correct answer is option 'D'. Can you explain this answer?

Direction of vector product of 2 vector is perpendicular to both vector
means if A×B=C then C is perpendicular to A as well as B .
now apply this concept on your question
let B×A=C ,
A.(B×C)=A.C
where C is perpendicular to both vector A&B
so angle b/w C and A is 90
A.C=0

A particle moves in a circle of radius 5 cm with constant speed and time period 0.2πs. The acceleration of the particle is [2011]
  • a)
    15 m/s2
  • b)
    25 m/s2
  • c)
    36 m/s2
  • d)
    5 m/s2
Correct answer is option 'D'. Can you explain this answer?

Simran Nair answered
To find the speed of the particle, we can use the formula:

speed = distance / time

Since the particle moves in a circle, the distance it travels in one complete revolution is the circumference of the circle, which is 2πr, where r is the radius of the circle.

Given that the radius is 5 cm, the distance the particle travels in one complete revolution is:

distance = 2π(5 cm) = 10π cm

Since the time period is 0.2 seconds, the time it takes for the particle to complete one revolution is 0.2 seconds.

Therefore, the speed of the particle is:

speed = distance / time = (10π cm) / (0.2 s) = 50π cm/s

So, the speed of the particle is 50π cm/s.

A bullet is fired from a gun with a speed of 1000 m/s in order to hit a target 100 m away. At what height above the target should the gun be aimed? (The resistance of air is negligible and g = 10 m/s2) [1995]
  • a)
    5 cm
  • b)
    10 cm
  • c)
    15 cm
  • d)
    20 cm
Correct answer is option 'A'. Can you explain this answer?

Raghav Khanna answered
Speed of the bullet (v) = 1000 m/s and horizontal distance of the target (s) = 100 m.
Time taken to cover the horizontal distance
During this time, the bullet will fall down vertically due to gravitational acceleration.

A stone tied to the end of a string of 1 m long is whirled in a horizontal circle with a constant speed. If the stone makes 22 revolutions in 44 seconds, what is the magnitude and direction of acceleration of the stone? [2005]
  • a)
    π2 ms–2 and direction along the radius towards the centre
  • b)
    π2 ms–2 and direction along the radius away from the centre
  • c)
    π2 ms–2 and direction along the tangent to the circle
  • d)
    π2/4 ms–2 and direction along the radius towards the centre
Correct answer is option 'A'. Can you explain this answer?

First, we need to find the angular velocity (ω) of the stone:
Number of revolutions = 22
Time taken = 44 seconds
Therefore, frequency (f) = number of revolutions / time taken = 22/44 = 0.5 Hz
Angular velocity (ω) = 2πf = 2π(0.5) = π rad/s

Next, we can use the formula for centripetal acceleration (ac) to find the magnitude of acceleration:
ac = ω2r
where r is the radius of the circle (1 m).
ac = (π)2(1) = 9.87 m/s2

The direction of acceleration is towards the center of the circle (i.e. radially inward).

Therefore, the magnitude of acceleration of the stone is 9.87 m/s2 and the direction is radially inward.

A body of mass 0.4 kg is whi rled in a vertical circle making 2 rev/sec. If the radius of the circle is 1.2 m, then tension in the string when the body is at th e top of the circle, is [1999]
  • a)
    41.56 N
  • b)
    89.86 N
  • c)
    109.86 N
  • d)
    115.86 N.
Correct answer is option 'A'. Can you explain this answer?

Raghav Khanna answered
Given : Mass (m) = 0.4 kg Its frequency (n) = 2 rev/sec Radius (r) =1.2 m.
We know that linear velocity of the body (v) = ωr = (2πn)r                
= 2 × 3.14 × 1.2 × 2 = 15.08 m/s.
Therefore, tension in the string when the body is at the top of the circle (T)
= 45.78 - 3.92 = 41.56 N

A ball of mass 0.25 kg attached to the end of a string of length 1.96 m is moving in a horizontal circle. The string will break if the tension is more than 25 N. What is the maximum speed with which the ball can be moved? [1998]
  • a)
    14 m/s
  • b)
    3 m/s
  • c)
    5 m/s
  • d)
    3.92 m/s
Correct answer is option 'A'. Can you explain this answer?

Given data:
Mass of the ball, m = 0.25 kg
Length of the string, l = 1.96 m
Maximum tension, T = 25 N

Formula:
The centripetal force required to keep the ball moving in a circle is provided by the tension in the string. This can be calculated using the formula:
T = mv^2 / r
where T is the tension, m is the mass of the ball, v is the speed of the ball, and r is the radius of the circle (which is equal to the length of the string).

Calculations:
Given that the maximum tension is 25 N, we can rearrange the formula to find the maximum speed:
25 = 0.25 * v^2 / 1.96
v^2 = 25 * 1.96 / 0.25
v^2 = 196
v = √196
v = 14 m/s
Therefore, the maximum speed with which the ball can be moved is 14 m/s. Hence, option 'A' is correct.

A stone tied with a string, is rotated in a vertical circle. The minimum speed with which the string has to be rotated [1999]
  • a)
    is independent of the mass of the stone
  • b)
    is independent of the length of the str ing
  • c)
    decreases with increasing mass of the stone
  • d)
    decreases with in creasing length of the string
Correct answer is option 'A'. Can you explain this answer?

Palak Basu answered
The Minimum Speed Required for a Stone in Vertical Circle

The problem is about finding the minimum speed required for a stone attached to a string to move in a vertical circle. The answer is option 'A', which means that the minimum speed is independent of the mass of the stone. Here's how we can arrive at this conclusion:

Force Analysis

When the stone is moving in a vertical circle, it experiences two types of forces: tension and gravity. At the top of the circle, the tension force is directed downwards, while the gravity force is directed downwards as well. At the bottom of the circle, the tension force is directed upwards, while the gravity force is directed downwards as well.

Minimum Speed

To keep the stone moving in a circular path, the tension force must be larger than the gravity force at all points in the circle. Therefore, the minimum speed required for the stone to move in a vertical circle is the speed that makes the tension force just equal to the gravity force at the top of the circle.

Mathematical Analysis

Let's assume that the mass of the stone is m, the length of the string is L, and the speed of the stone is v. Then, the tension force T and the gravity force mg are given by:

T = mv^2/L

mg = m g

where g is the acceleration due to gravity. Equating these two forces at the top of the circle, we get:

mv^2/L = m g

which simplifies to:

v^2 = g L

Therefore, the minimum speed required for the stone to move in a vertical circle is:

v = √(g L)

Conclusion

The minimum speed required for a stone attached to a string to move in a vertical circle is independent of the mass of the stone. This is because the mass of the stone cancels out in the equation for the minimum speed. Therefore, the answer is option 'A'.

Which of the following is not a vector quantity?
  • a)
    sp eed
  • b)
    velocity [1995]
  • c)
    torque
  • d)
    displacement
Correct answer is option 'A'. Can you explain this answer?

Ruchi Chopra answered
A vector quantity has both magnitude and direction. In the given options, speed has only magnitude, therefore, it is non- vector or scalar quantity.

Three forces acting on a body are shown in the figure. To have the resultant force only along the y- direction, the magnitude of the minimum additional force needed is: [2008]
  • a)
    0.5 N
  • b)
    1.5 N
  • c)
  • d)
Correct answer is option 'A'. Can you explain this answer?

Dipanjan Mehta answered
Th e componen ts of 1N and 2N forces along + x axis = 1 cos60° + 2 sin30°
The component of 4 N force along –x-axis
Therefore, if a force of 0.5N is applied along + x-axis, the resultant force along x-axis will become zero and the resultant force will be obtained only along y-axis.

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