The change in frequency is called the Doppler effect. The speed of the car can be calculated by the formula for the Doppler effect for when the observer is standing still and the source of the sound is moving towards him:
f¹={V/(V-Vs)}*f,
where f¹ is the frequency of the car while moving towards the observer, V=343 m/s is the speed of sound, Vs is the speed of the car and f is the frequency of the car while standing still.
We need to solve the equation for the Vs:
f¹/f=V/(V-Vs)
V-Vs=V/(f/f¹)
-Vs=V/(f/f¹)-V
Vs=-V/(f/f¹)+V= -343/(300/330)+343=-343*0.91+343=-312.1+343=30.9 m/s
So the speed of the moving police car is Vs=30.9 m/s.
When balanced forces act on an object at rest, the object will not move. If you push against a wall, the wall pushes back with an equal but opposite force. Neither you nor the wall will move. Forces that cause a change in the motion of an object are unbalanced forces.
Unlike fixed joints or cartilaginous joints, where the bones are connected by either connective tissue or cartilage, the bones in synovial joints are not directly joined by anything, which allows for a much greater range of motion.
Answer:
There is a net force of 2 N to the left.
With 8 N to the left the up/down and left/right forces are in balance.
The force left over is 2 N to the left.