Relative Motion | MCQs

Explanation

When two bodies are moving in opposite directions, their velocities are added to find the relative velocity.

Let's say the velocities of the two bodies are v1 and v2.

Relative velocity = v1 + v2

Since both velocities are non-zero and in opposite directions, the relative velocity will be greater than the absolute velocity of either body.

So, the statement "Relative velocity > Absolute velocity" is true.

Explanation

When moving with constant velocity, there is no net acceleration acting on the body.

Therefore, the apparent weight remains the same as actual weight — not changed.

Explanation

Total distance = Length of train + Length of bridge = 100 m + 200 m = 300 m  

Speed = 15 m/s  

Time = Distance / Speed = 300 / 15 = 20 seconds

Explanation

I dropped ⇒ initial velocity =0

⇒ time will be given by h=12gt^2

t=√2hg=√2×20 m10 m/s^2=2 sec

II both reaches simultaneously be so ti,e taken by IInd stone will be 

2 sec−1 sec=1 sec

or t′=1 sec

putting it in h=ut'+12gt^2

& h=20 m,g=10m/s^2

we get 

20=u×1+5×1

⇒u=15 m/s

Explanation

When Bilal moves away from a stationary organ producing a sound of frequency 'f' with a speed equal to 0.5 times the speed of sound, he will hear a sound of lower frequency.

This phenomenon is known as the Doppler effect.

To calculate the frequency of the sound Bilal hears, we can use the following formula:

f' = f * (v + vL) / (v + vS)

Where:

- f' is the frequency of the sound heard by Bilal

- f is the frequency of the sound produced by the stationary organ

- v is the speed of sound

- vL is the speed of Bilal

- vS is the speed of the source (in this case, the stationary organ)

Since Bilal is moving away from the source, vS is negative.

We substitute the values into the formula:

f' = f * (v - 0.5v) / (v - (-v))

Simplifying the equation:

f' = f * (0.5v) / (2v)

f' = f * 0.5 / 2

f' = f * 0.25