Question

Ask Your Teacher A spotlight on the ground shines on a wall 12 m away. If a man 2 m tall walks from the spotlight toward the building at a speed of 1.1 m/s, how fast is the length of his shadow on the building decreasing when he is 4 m from the building? (Round your answer to one decimal place.)

Answer 1

Answer: 7.3seconds

Step-by-step explanation:

Using the echo concept, before echo can occur, we must have an object making the sound (the teacher), the diatance between the object and the reflector (x)(i.e the wall), the time taken for the shadow to disappear (t) and the velocity of sound /movement of the object (v). Using the relationship 2x = vt

According to the question, x = 12m (initial distance), v = speed of object t = time of disappearance.

We have time before disappearance calculated as 2 × 12/1.1 = 21.8s

When he is 4m from the building, it will there take 4 × 21.8/12 = 7.3seconds for his shadow to decrease on the way.