smc-4746-50-Real world applications

v1 Measurement, STD2 M7 2008 HSC 20 MC

A point `P` lies between a lamp post, 1.5 metres high, and a building, 7 metres high. `P` is 2.5 metres away from the base of the post.

From `P`, the angles of elevation to the top of the lamp post and to the top of the building are equal.

What is the distance, `x`, from `P` to the top of the tower?

10.60
12.50
13.60
14.55

Show Answers Only

`C`

Show Worked Solution

`text(Triangles are similar)\ \ text{(equiangular)}`

`text(In smaller triangle:)`

`h^2`	`= 1.5^2 + 2.5^2`
	`= 8.5`
`h`	`= sqrt 8.5`

`x/sqrt8.5`	`= 7/1.5 \ \ \ text{(sides of similar Δs in same ratio)}`
`x`	`= (7 sqrt 8.5)/1.5`
	`= 13.60…`

`=> C`

v1 Measurement, STD2 M7 2016 HSC 16 MC

The width (`W`) of a road can be calculated using two similar triangles, as shown in the diagram.

What is the approximate width of the road?

`12.8\ text(m)`
`13.3\ text(m)`
`14.6\ text(m)`
`17.8\ text(m)`

Show Answers Only

`=> C`

Show Worked Solution

`text{Triangles are similar (equiangular)}`

`text(Using similar ratios:)`

`W/(6.5)`	`= 18/8`
`:. W`	`= (18 xx 6.5)/8`
	`= 14.62…`

`=> C`

Similarity, SMB-004

A traffic light is 2.4 m tall. Its shadow from a nearby floodlight is 3 m long.

What is the height of the floodlight? (3 marks)

Show Answers Only

`text(4.0 m)`

Show Worked Solution

`text{Triangles share common angle and both have right angles}`

`=>\ text{Triangles are similar (equiangular)}`

`text{Since corresponding sides are in similar ratios:}`

`h/5`	`= 2.4/3`
`:. h`	`= (5 xx 2.4)/3`
	`= 4\ text(metres)`

Measurement, STD2 M7 2016 HSC 16 MC

The width (`W`) of a river can be calculated using two similar triangles, as shown in the diagram.

What is the approximate width of the river?

`17.8\ text(m)`
`19.3\ text(m)`
`23.2\ text(m)`
`24.9\ text(m)`

Show Answers Only

`=> A`

Show Worked Solution

`text{Triangles are similar (equiangular)}`

`text(Using similar ratios:)`

`W/(7.1)`	`= 20.3/8.1`
`:. W`	`= (20.3 xx 7.1)/8.1`
	`= 17.79…`

`=> A`

Measurement, STD2 M7 2015 HSC 27a

At a particular time during the day, a tower of height 19.2 metres casts a shadow. At the same time, a person who is 1.65 metres tall casts a shadow 5 metres long.

What is the length of the shadow cast by the tower at that time? (2 marks)

--- 4 WORK AREA LINES (style=lined) ---

Show Answers Only

`58\ text{m}`

Show Worked Solution

`text(Both triangles have right angles and a common)`

`text(angle to the ground.)`

`:.\ text{Triangles are similar (equiangular)}`

`text(Let)\ x =\ text(length of tower shadow)`

`x/5`	`= 19.2/1.65\ \ text{(corresponding sides of similar triangles)}`
`x`	`= (5 xx 19.2)/1.65`
	`= 58.1818…`
	`= 58\ text{m (nearest m)}`

Measurement, STD2 M7 2008 HSC 20 MC

A point `P` lies between a tree, 2 metres high, and a tower, 8 metres high. `P` is 3 metres away from the base of the tree.

From `P`, the angles of elevation to the top of the tree and to the top of the tower are equal.

What is the distance, `x`, from `P` to the top of the tower?

9 m
9.61 m
12.04 m
14.42 m

Show Answers Only

`D`

Show Worked Solution

`text(Triangles are similar)\ \ text{(equiangular)}`

`text(In smaller triangle:)`

`h^2`	`= 2^2 + 3^2`
	`= 13`
`h`	`= sqrt 13`

`x/sqrt13`	`= 8/2\ \ \ text{(sides of similar Δs in same ratio)}`
`x`	`= (8 sqrt 13)/2`
	`= 14.422…`

`=> D`

Measurement, STD2 M7 2012 HSC 28c

Jacques and a flagpole both cast shadows on the ground. The difference between the lengths of their shadows is 3 metres.

What is the value of `d`, the length of Jacques’ shadow? (3 marks)

--- 6 WORK AREA LINES (style=lined) ---

Show Answers Only

`d = 1.8\ text(m)`

Show Worked Solution

♦♦ Mean mark 24%

`text{Both triangles have right-angles with a common (ground) angle.}`

`:.\ text{Triangles are similar (equiangular)}`

` text{Since corresponding sides are in the same ratio}`

`d/1.5`	`= (d+3)/4`
`4d`	`= 1.5(d + 3)`
`8d`	`= 3(d + 3)`
	`= 3d + 9`
`5d`	`= 9`
`:.d`	`= 9/5`
	`=1.8\ text(m)`