Question

A truck travels some distance at a speed of 35 km h in 120 min and the remaining distance at a speed of 48 km h in 90 min. Determine the: (a) total distance covered. (b) average speed over the entire journey​

Answer 1

(a) 142 km

(b) 40.57 km/h (2 d.p.)

Explanation:

Part (a)

`\boxed{\sf Distance=Speed * Time}`

Given:

• Speed = 35 km/h
• Time = 120 min = 2 h

Substitute the given values into the distance formula to find the distance travelled:

`\implies \sf Distance = 35 * 2 = 70\;km`

Given:

• Speed = 48 km/h
• Time = 90 min = 1.5 h

Substitute the given values into the distance formula to find the distance travelled:

`\implies \sf Distance = 48 * 1.5 = 72\;km`

Therefore, the total distance travelled is:

`\implies \sf 70 + 72 = 142 \; km`

Part (b)

`\boxed{\sf Average\;speed=(Total\;distance)/(Total\;time)}`

Given:

• Total distance = 142 km
• Total time = 2 + 1.5 = 3.5 h

Substitute the given values into the average speed formula to find the average speed over the entire journey:

`\implies \sf Average\:speed=(142)/(3.5)=40.57\;km/h\;(2\;d.p.)`

Answer 2

• a) 142 km,
• b) 40.57 km/h

Explanation:

Use of formula:

• speed = distance / time
• distance = speed × time

a) Find each part of distance and add together. Convert minutes to hours.

• 35 × (120/60) = 35 × 2 = 70 km,
• 48 × (90/60) = 48 × 1.5 = 72 km

• distance = 70 + 72 = 142 km

b) Average speed is:

• speed = 142 /(2 + 1.5) = 142/3.5 = 40.57 km/h (rounded)