﻿ An earthquake generates both transverse (S) and longitudinal (P) sound waves in the earth. The speed of S waves is about 4.5 km/s and that of P waves is about 8.0 km/s. A seismograph records P and S waves from an earthquake. The first P wave arrives 4.0 min before the first S wave. The epicentre of the earthquake is located at a distance about | Motion in Straight Line

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# Motion in Straight Line

#### Multiple Choice Questions

121.

From the top of a tower, 80 m high from the ground, a stone is thrown in the horizontal direction with a velocity of 8 ms-1 . The stone reaches the ground after a time 't' and falls at a distance of 'd' from the foot of the tower. Assuming g = 10 m/s2, the time t and distance d are given respectively by

• 6 s, 64 m

• 6 s, 48 m

• 4 s, 32 m

• 4 s, 16 m

122.

A particle moves with constant acceleration along a straight line starting from rest. The percentage increase in its displacement during the 4th second compared to that in the 3rd second is

• 33 %

• 40 %

• 66 %

• 77 %

123.

Particle A moves along X-axis with a uniform velocity of magnitude 10 m/s. Particle B moves with uniform velocity 20 m/s along a direction making an angle of 60° with the positive direction of X-axis as shown in the figure. The relative velocity of B with respect to that of A is

• 10 m/s along X-axis

•  m/s along Y-axis (perpendicular to X-axis)

• $10\sqrt{5}$ m/s along the bisection of the velocities of A and B

• 30 m/s along negative X-axis

124.

A cylinder of height h is filled with water and is kept on a block of height h/2. The level of water in the cylinder is kept constant. Four holes numbered 1,2, 3 and 4 are at the side of the cylinder and at heights 0, h/4, h/2 and 3h/4, respectively. When all four holes are opened together, the hole from which water will reach farthest distance on the plane PQ is the hole number

• 1

• 2

• 3

• 4

125.

A ball is thrown vertically upwards. Which of the following  plots represents the speed-time graph of the ball during its flight if the air resistance is not ignored?

# 126.An earthquake generates both transverse (S) and longitudinal (P) sound waves in the earth. The speed of S waves is about 4.5 km/s and that of P waves is about 8.0 km/s. A seismograph records P and S waves from an earthquake. The first P wave arrives 4.0 min before the first S wave. The epicentre of the earthquake is located at a distance about25 km 250 km 2500 km 5000 km

C.

2500 km

Velocity of the S wave is v1 = 4.5 km/s

The velocity of the P waves is v2 = 8.0 km/s

Let the time taken by the S and P waves to reach the seismograph be t1 and  t2

It is given that

t1 $-$ t2 = 4 min

= 4 × 60 sec

t1 $-$ t2 = 240 sec              .....(i)

Let the distance of the epicentre (km) be S. Then

S = v1t1 = v2t2

⇒  4.5 × t1 $-$ 8t2 = 0

⇒              t1$\frac{4.5}{8}$t1            ....(ii)

Using (i) and (ii)

t1 $-$ t2 = 240

⇒   t1  = 240

⇒     t1

⇒          = 548.5 s

∴      S = v1t1

= 4.5 × 548.5

S = 2468.6

S ≈ 2500 km