Question 7
If the amplitude of a body in SHM becomes one-half of the initial value, what would be the ratio
between the final total energy and initial total energy?
A. 1:2
B. 1:1
C. 2:1
D. 1:4
E. 4:1
Correct Answer: D
Explanation:
Total energy of a body in SHM is given as
E = (1/2)kA
2
------------- (1)
Initial energy is given by E
1
= (1/2)kA
1
2
----------------- (2)
Final energy is given by E
2
= (1/2)kA
2
2
---------------- (3)
Since A
2
= A
1
/ 2, E
2
= (1/4)[(1/2)kA
1
2
] ---------------- (5)
Comparing equation 5 with 2 we get
E
2
: E
2
= 1 : 4
Therefore, D is the correct answer option.
Question 8
A seismic wave originates at point A and travels along every direction with a speed of 1.6 m/s.
If the seismic wave reaches a point B which is at a distance of 2000 Km from A, what would be
the time difference between the points A and Bin minutes?
A. 20.83 minutes
B. 18.57 minutes
C. 15.78 minutes
D. 21.56 minutes
E. 19.56 minutes
Correct Answer: A
Explanation:
A seismic wave originates at point A, travels along every direction and reaches point B. As it
originates from A, it will reach point B after some timeandthis is thetime difference. Time difference
can be given as
Time difference = distance / speed -------------- (1)
Distance between A and B is given as 2000 Km and speed of the seismic wave = 1.6 km/s. Therefore,
putting these values in equation 1 we get
