A wave pulse travels along a stretched string at a speed of 200 cm/s. What will be the speed if: a. The string's tension is doubled?
b. The string's mass is quadrupled (but its length is unchanged)?
c. The string's length is quadrupled (but its mass is unchanged)?
d. The string's mass and length are both quadrupled?

a. 282.84 cm/s b. 100 cm/s c. 400 cm/s d. 200 cm/s

Explanation:

The speed of the wave v = √(T/μ) where T = tension and μ = mass per unit length = m/l where m = mass of string and l = length of string.

So, v = √(T/μ)

v = √(T/m/l)

v = √(Tl/m)

a. The string's tension is doubled?

If the tension is doubled, T' = 2T the new speed is

v' = √(T'l/m)

v' = √(2Tl/m)

v' = √2(√Tl/m)

v' = √2v

v' = √2 × 200 cm/s

v' = 282.84 cm/s

b. The string's mass is quadrupled (but its length is unchanged)?

If the mass is quadrupled, m' = 4m the new speed is

v' = √(Tl/m')

v' = √(Tl/4m)

v' = (1/√4)(√Tl/m)

v' = v/2

v' = 200/2 cm/s

v' = 100 cm/s

c. The string's length is quadrupled (but its mass is unchanged)?

If the length is quadrupled, l' = 4l the new speed is

v' = √(Tl'/m)

v' = √(T(4l)/m)

v' = √4)(√Tl/m)

v' = 2v

v' = 200 × 2 cm/s

v' = 400 cm/s

d. The string's mass and length are both quadrupled?

If the length is quadrupled, l' = 4l and mass quadrupled, m' = 4m, the new speed is

v' = √(Tl'/m')

v' = √(T(4l)/4m)

v' = √(Tl/m)

v' = v

v' = 200 cm/s

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