Relative Motion in One Dimension - NEET Physics Questions
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Relative Motion in One Dimension

Question 1:

A 100 m long train at 15 m/s overtakes a man running on the platform in the same direction in 10s. How long the train will take to cross the man if he was running in the opposite direction ?

1. 7 s
2. 5 s
3. 3 s
4. 1 s
View Answer

1. Relative Speed (Same Direction):
\[
\text{Speed of Train} = 15 \, \text{m/s}
\]
\[
\text{Time to Overtake} = 10 \, \text{s}
\]
\[
\text{Distance} = \text{Length of Train} = 100 \, \text{m}
\]
\[
\text{Relative Speed} = \frac{\text{Distance}}{\text{Time}} = \frac{100}{10} = 10 \, \text{m/s}
\]
\[
\text{Speed of Man} = 15 - 10 = 5 \, \text{m/s}
\]

2. Relative Speed (Opposite Direction):
\[
\text{Relative Speed} = 15 + 5 = 20 \, \text{m/s}
\]

3. Time to Cross Man (Opposite Direction):
\[
\text{Time} = \frac{\text{Distance}}{\text{Relative Speed}} = \frac{100}{20} = 5 \, \text{s}
\]

Thus, the train will take 5 seconds to cross the man if he is running in the opposite direction.

Question 2:

Two cars are moving along a straight line in opposite direction with the same speed 10 m/s. The relative velocity of two cars w.r.t. each other is:

1. 20 m/s
2. 30 m/s
3. zero
4. none of these
View Answer

When objects move in opposite directions relative velocity= v1+ v2= 20 m/s

Question 3:

Two objects A and B are moving with speeds 10 m/sĀ  and 20 m/s respectively in the same direction. The relative velocity of A w.r.t. B is

1. 30 m/s
2. 10 m/s
3. - 10 m/s
4. 50 m/s
View Answer

When moving in same direction relative velocity = V 1 -V 2= 10-20 = -10 m/s

Question 4:

Two objects A and B are moving with speeds 10 m/s and 20 m/s respectively in the same direction. The relative velocity of B w.r.t. A is

1. 30 m/s
2. 10 m/s
3. - 10 m/s
4. 50 m/s
View Answer

Velocity of A w.r.t B = V A - V B
Velocity of B w.r.t A = V B - V A

Question 5:

The relative velocity of two objects A and B is 10 m/s. If the velocity of object A is 40 m/s then the velocity with which B is moving is (assume both objects are moving in same direction)

1. 10 m/s
2. 20 m/s
3. 30 m/s
4. 40 m/s
View Answer

Relative Velocity = V A - V B
10= 40 - V B
V B = 30 m/s

* Is 50 m/s a possible answer ?

Question 6:

Two trains A and B are moving in a straight line in the same direction with speeds of 54 km/h and 15 m/s respectively. The relative velocity of one train w.r.t. other is

1. 69 km/hr
2. 69 m/s
3. 39 m/s
4. Zero
View Answer

As, 54 km/hr = 15 m/s both have same velocity in same direction their relative speed/velocity is zero

Question 7:

Two objects A and B are moving in same direction with same speed of 20 m/s each then, which of the following position-time graphs correctly represents two moving objects A and B

neet question in 1-d motion

1. 1
2. 2
3. 3
4. 4
View Answer

As both A and B have same velocity their relative speed is zero. so both have same slope in position time graph.