 # [Trigonometry] HnD Type #5: Finding speed, time or distance made easy for SSC

In Aptitude by Support Staff

# Introduction

Continuing in the series of “Trigonometry –>Height and Distance(HnD)–> Five types of Questions.

5th and the last type of question is “finding speed, time or distance”. Here are example questions (both solved in the video)

1. A jet is flying at a constant height of 4500 root 3meters. Angle of elevation of the jet from a point on ground is 60 Degrees. After 30 seconds of flight, this angle becomes 30 degrees. Find speed of this jet plane.
2. A car is 60m away from a building. Angle of elevation is 45. After 5 seconds, car moves away from the building and angle is decreased to 30. Find speed of this car.

# Approach

• Basically approach is same as “one building two angles” type of questions.= Since two angles are given, you make two equations of “TAN” using Topi-triangle shortcutTM and you get a distance.
• Then apply “STD” formula (speed x time = distance) and you’ll get the answer.
• Check the following video to see it in detail and after watching the video, solve the mock questions given at the bottom of this article.

If the video is not visible, check it directly on youtube by clicking me

# Mock questions 1. A 1.3 m tall man spots a balloon moving with the wind in a horizontal line at a constant height of 91.3 m above the ground. The angle of elevation of this balloon is 60°. After some time the angle is reduced to 30°. Find the distance travelled by the balloon during this interval
2. From a 100m tall lighthouse, the angle of depression of a ship is 30. After some time, angle of depression increases to 45. Find the distance travelled by ship during this time interval. (hint: STD formula unnecessary here!)
3. A man on the top of building observes a car moving at a uniform speed and coming directly towards the building.  it takes 12 minutes for the angle of depression to change from 30 to 45, how soon after this, will the car reach the building?