Question

A motor cycle starts from rest and accelerates along a straight path at 2 m/s². At the starting point of the motor cycle there is a stationary electric siren. How far has the motor cycle gone when the driver hears the frequency of the siren at 94% of its value when the motor cycle was at rest ? (Speed of sound = 330 ms^–1)

• A. 49 m
• B. 98 m
• C. 147 m
• D. 196 m

Answer 1

Answer: (B)

98 m

Answer 2

When source in stationary and observer is

moving away from the source.

n' = n $\left( \frac { \mathrm { V } - \mathrm { V } _ { 0 } } { \mathrm {~V} } \right)$

Ž 0.94 n = n $\left( \frac { 330 - \mathrm { V } _ { 0 } } { 330 } \right)$

Ž V₀ = 19.8 m/s

V₀² = 0 + 2as

$\frac { 5400 \times 100 } { 90 }$ S =

= $\frac { 19.8 \times 19.8 } { 2 \times 2 }$

= 98 m.