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# Kinematics Good conceptual problems

Kinematics is an important topic in Physics. Here I have some Kinematics Good conceptual problems to help you learn kinematics and its concept

Question:
If you are riding on a train that speeds past other train moving in the same direction on adjacent train. It appears the other train is moving backward. Why?

Solution:
Your reference frame is that of the train you are riding. If you are traveling with a relatively constant velocity (not over a hill or around a curve or drastically changing speed), then you will interpret your reference frame as being at rest. Since you are moving forward faster than the other train, the other train is moving backwards relative to you. Seeing the other train go past your window from front to rear makes it look like the other train is going backwards. This is similar to passing a semi truck on the interstate out of a passenger window, it looks like the truck is going backwards.

Question:
A package is dropped from the plane. Four People sitting in the plane make different statements about the package location when it hits the ground. Air resistance can be ignored

Person A: The package will fall behind the plane
Person B: The package remain below the plane until it hit the ground
Person C:The package move ahead of the plane
Person D: The package location will depend on the speed of the plane

We know that only one person is correct and three are wrong
Who are those three person’s
A) Person A,B,C
b) Person A,C,D
c) Person B,C,D
d) Person A,B,D

Solution:
The package will have same horizontal velocity as of plane.The vertical velocity will be dictated by the force of gravity.
So it will cover the same horizontal distance as plane before hitting the ground.So Person B is correct

Question:
Jack and Henry both are good swimmer and can swim with same speed in still water . They setoff across the river at the same time.
Jack moves straight across and Jack is pulled downstream by the current somewhat.Henry heads upstream at an angle so as to arrive at a point directly opposite to starting point .

Who will cross the river first?
A) jack

b) henry

c) Both Jack and Henry will cross the river in same time

Solution:

Both jack and henry need to cover the same “cross river” distance. The swimmer with the greatest speed in the “cross river” direction will be the one that reaches the other side first.The current has no bearing on the problem because the current doesn’t help either of the boats move across the river.
Thus the swimmer heading straight across will reach the other side first. All of his swiming effort has gone into crossing the river. For the upstream swimmer, some of his swimming effort goes into battling the current,and so his “cross river” speed will be only a fraction of his swimming speed.So Jack will come first

Question:

During projection motion,the velocity and acceleration vectors are acting in different direction at different points.

Which of the following is true

a) v.a =0 at the topmost point

b) v.a < 0 during the upward journey

c) v.a > 0 during the downward journey

d) None of these

Solution:

During Upward journey

v=vxi+vyj

g=-gj

v.a < 0

At topmost point

v=vxi

g=-gj

v.a =0

During downward journey

v=vxi-vyj

g=-gj

v.a > 0

Question:

An elevator starts from rest and accelerates upwards for some time until it reaches its cruising speed. It then travels at constant speed for a while and finally decelerates to stop at the desired floor. Describe the velocity-time and position-time graphs for the elevator’s motion. Explain how the acceleration is related to the slopes of these graphs.

Solution:

• Velocity-time graph: The graph starts with a positive slope (acceleration) until the elevator reaches cruising speed, then it continues horizontally (constant speed), and ends with a negative slope (deceleration).
• Position-time graph: The graph is a curve that starts steep and flattens as the elevator moves at constant speed, then curves again as it decelerates to stop.
• Acceleration: During acceleration and deceleration, the graph slopes are positive and negative, respectively. When moving at constant speed, acceleration is zero, reflecting a flat section on the velocity-time graph.

Question:

How would the trajectory of a projectile (like a ball thrown at an angle) change if you were on the Moon instead of the Earth? Consider differences in gravitational acceleration and neglect air resistance. How does the maximum height, time of flight, and range of the projectile change?

Solution

• On the Moon, where gravity is weaker than on Earth, a projectile would travel farther and higher and spend more time in the air because the gravitational acceleration (which pulls the projectile back to the surface) is less.
• The maximum height and time of flight increase, while the gravitational pull affects the range, making it longer on the Moon compared to Earth.

Question:

A ball is dropped from a certain height above the ground. Without air resistance, how does its velocity and position change with time? If at the same instant the ball is dropped, another ball is thrown horizontally from the same height, which ball hits the ground first, or do they hit the ground at the same time?

Solution

Both balls hit the ground at the same time. This is because the vertical motion (affected by gravity) is independent of the horizontal motion. Both balls experience the same vertical acceleration due to gravity and start from the same height, so their vertical motion is identical despite the horizontal throw of one ball.

Question:

In a circular swing ride, the direction of the centripetal acceleration is:
A) Tangent to the circular path
B) Opposite to the direction of motion
C) Towards the center of the circle
D) Away from the center of the circle

Solution

The velocity vector is always tangent to the circle, pointing in the direction of motion. The acceleration vector (centripetal acceleration) points towards the center of the circle. Hence (c) is the correct option

Question:

A person is running on a moving walkway (such as those found in airports) that is moving in the same direction as the runner. If a runner runs at a speed of 3 m/s on a walkway moving at 2 m/s in the same direction, the runner’s speed relative to the ground is:
A) 1 m/s
B) 3 m/s
C) 5 m/s
D) 6 m/s

Solution

The speed of the runner relative to the ground is the sum of the speed of the runner relative to the walkway and the speed of the walkway relative to the ground. Hence the answer is (C). This illustrates the concept of relative velocity, showing that the runner moves faster relative to the ground when on the moving walkway than when running on stationary ground at the same speed relative to the walkway.

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