Q. A train leaves a station and travels at 90 km/h. Another train leaves the same station 30 minutes later and travels at 120 km/h. How far from the station will they meet?
A.
90 km
B.
120 km
C.
150 km
D.
180 km
Solution
Let the distance be d. Time taken by first train = d/90. Time taken by second train = d/120. Setting up the equation gives d = 150 km.
Q. A train leaves a station at 80 km/h and another train leaves the same station 30 minutes later at 100 km/h. How far from the station will they meet?
A.
100 km
B.
120 km
C.
150 km
D.
180 km
Solution
Let the time taken by the first train be t hours. Distance = speed * time. 80t = 100(t - 0.5). Solving gives t = 2 hours, so distance = 80 * 2 = 160 km.
Q. A train moving at 72 km/h passes a platform 300 m long. How long does it take to cross the platform completely?
A.
10 seconds
B.
15 seconds
C.
20 seconds
D.
25 seconds
Solution
Total distance = Length of train + Length of platform. If length of train is L, time = (L + 300)/20 m/s. Assuming L = 300 m, time = (300 + 300)/20 = 30 seconds.
Q. A train travels at a speed of 90 km/h and a car at 60 km/h. If they start from the same point and travel in the same direction, how far apart will they be after 1 hour?
A.
30 km
B.
20 km
C.
10 km
D.
40 km
Solution
Relative speed = 90 - 60 = 30 km/h. Distance apart after 1 hour = 30 km.
Q. If a car travels at a speed of 80 km/h and a bike travels at 60 km/h, how far apart will they be after 1 hour if they start from the same point and travel in the same direction?
A.
20 km
B.
30 km
C.
40 km
D.
50 km
Solution
Relative speed = 80 - 60 = 20 km/h. Distance apart after 1 hour = 20 km.
Q. Two cars start from the same point and travel in opposite directions. If car A travels at 70 km/h and car B at 50 km/h, how far apart will they be after 2 hours?
A.
240 km
B.
220 km
C.
200 km
D.
180 km
Solution
Relative speed = 70 + 50 = 120 km/h. Distance apart after 2 hours = 120 * 2 = 240 km.
Q. Two cars start from the same point and travel in opposite directions. If car A travels at 40 km/h and car B at 60 km/h, how far apart will they be after 1 hour?
A.
50 km
B.
80 km
C.
100 km
D.
120 km
Solution
Relative speed = 40 + 60 = 100 km/h. Distance apart after 1 hour = 100 km.
Q. Two observers are moving towards each other at speeds of 20 m/s and 30 m/s. What is the relative velocity of one observer with respect to the other?
A.
10 m/s
B.
20 m/s
C.
50 m/s
D.
60 m/s
Solution
Relative velocity = Velocity of observer 1 + Velocity of observer 2 = 20 m/s + 30 m/s = 50 m/s.
Understanding "Relative Motion" is crucial for students preparing for school and competitive exams in India. This topic not only forms the basis of many physics concepts but also frequently appears in various examination formats. Practicing MCQs and objective questions on relative motion can significantly enhance your exam preparation, helping you identify important questions and improve your scoring potential.
What You Will Practise Here
Concept of relative velocity and its significance
Understanding frames of reference and their applications
Relative motion in one and two dimensions
Key formulas related to relative motion
Graphical representation of relative motion
Common scenarios involving moving objects
Problem-solving techniques for relative motion questions
Exam Relevance
The topic of relative motion is a staple in CBSE, State Boards, NEET, and JEE exams. Students can expect questions that assess their understanding of relative velocity, the application of formulas, and the ability to analyze motion from different frames of reference. Common question patterns include numerical problems, conceptual questions, and application-based scenarios, making it essential to master this topic for a solid performance in exams.
Common Mistakes Students Make
Confusing the concepts of absolute and relative velocity
Misinterpreting the direction of motion in different frames
Neglecting to apply the correct formulas in problem-solving
Overlooking the significance of diagrams in understanding motion
Failing to account for the effects of acceleration in relative motion problems
FAQs
Question: What is relative motion? Answer: Relative motion refers to the calculation of the motion of an object as observed from a particular frame of reference, which can differ based on the observer's own motion.
Question: How do I solve relative motion problems effectively? Answer: To solve relative motion problems, identify the frames of reference, apply the relevant formulas, and carefully analyze the direction of each object's motion.
Now that you have a clear understanding of relative motion, it's time to put your knowledge to the test! Solve practice MCQs and objective questions to reinforce your understanding and boost your confidence for the upcoming exams. Remember, consistent practice is the key to success!
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