Question

Fig. 6.1 shows a car suspension system.
The suspension system uses four identical coil springs.

(a) The weight of the car causes compression in the springs. The length of each spring is reduced
from its original length.
Hooke’s Law can be used for compression as well as extension:
       F = kx
where F = load, k = spring constant and x = compression.
The weight of the car is 17000N.
Each spring has a spring constant of 2500N/ cm.
Each spring is reduced to a length of 24cm.
Calculate the original length of each spring

(b) Ultrasound waves are used to check for cracks in the springs of the car.
Ultrasound waves are high-frequency sound waves.
(i) The frequency of the ultrasound waves is above the audible range of a healthy human ear.
Suggest a frequency for ultrasound waves.
                                                                                        frequency = ……………………………………………. Hz 
(ii) Ultrasound waves are longitudinal waves.
Complete the sentences about longitudinal waves.
Longitudinal waves are produced by vibrations which occur ………………………………….. to the direction of energy transfer.
Longitudinal waves travel through air in compressions and ………………………………….. .
(iii) A transmitted ultrasound wave travels through the metal of the spring and is reflected by a crack as shown in Fig. 6.2.

The reflected wave is detected after the transmitted wave is sent, as shown in Fig. 6.3.

The ultrasound wave travels at 5200m/s in the metal of the spring.
Use Fig. 6.3 to determine the distance to the crack.

                                          distance = …………………………………………….. m