For the following questions answer them individually
When a sound producing source moves with a speed higher than the sound, shock waves are
produced in air. What is the very sharp and loud sound produced by these shock waves called?
Two places—P and Q are 400 miles apart. A car starts from P at a speed of 50 mph towards Q. After 75 minutes, another car starts from Q to P at a speed of 40 mph. At what time will the cars meet?
In the following question, which one of the four interchanges in signs and numbers would make the given equation correct?7 $$\div$$ 2 - 4 + 1 = 6
