Wednesday, 15 September 2021 07:28

# Time, Speed and Temperature - Class 8 Mathematics Revision Notes

Time, Speed and Temperature

Worked Exercise

1. An airplane took 4½ hours to fly from Cairo to Zambia. If it landed in Nairobi at Nairobi at 0215 h on Saturday, when did it take off from Cairo?
1. Friday 2145 h
2. Saturday 2245h
3. Friday 2245h
4. Saturday 2145 h
Working
The time the aeroplane took from midnight to 0215h of Saturday = 2h 15min
The difference (4h 30min – 2h 15min) is the time the aero plane took on Friday night.
Time on Friday night
h         min
4         30
- 2         15
2         15
= 2h 15min before midnight
Time of takeoff from Cairo
h      min
24     00
- 2     15
21     45 on Friday
The correct answer is A (Friday 2145 h)
2. A train let Mombasa on Monday at 2125 h and took sixteen and half hours to reach
Kisauni. When did the train reach Kisumu?
1. Tuesday 1.55 a.m
2. Tuesday 1.55 p.m
3. Wednesday 1.55 p.m
4. Monday 1:55 a.m
Working
Monday: from 2125h to midnight = 2400h - 2125h
= 2h 35min
Tuesday: Number of hours traveled from midnight
= 16h 30min - 2h 35 min
= 13h 55min
The train arrived at Kisumu on Tuesday at 1355h
This is the same as 1.55p.m
The correct answer is B (Tuesday 1.55pm)
3. A meeting started at quarter to noon. If the meeting lasted for 2 h 35min, what time in 24-h clock system did the meeting end?
1. 1320h
2. 1420h
3. 1310h
4. 1410h
Working
The meeting started at 11.45
h       min
11       45
+ 2       35
14      20
The meeting ended at 1420h
The correct answer is B (1420 h)
4. A wall clock gains 3 seconds every one hour. The clock was set correct at 1pm on Tuesday. What time was it showing at 1pm on Friday on the following week?
Working
The number of days from Tuesday 1 pm to Friday 1pm the following week = 10days.
Number of hours = (24 x 10) = 240 hrs.
The clock gains 3 seconds after every hour in ten days.
240 x 3 = 720 seconds
Min = 720/60 = 12 min
Hence it will show 1 p.m. + 12 min = 1.12 pm
In 24 h clock system
= 1312h
The correct answer is B (1312h)
5. A cyclist traveled from Nairobi to Nyeri for 4h 30min at a speed of 80km/h. He drove back to Nairobi taking 4 hours. What is his speed, in km/h?
1. 90
2. 72
3. 80
4. 100
Working
Distance = speed x time
= 80 x 4½
= 360 km
From Nyeri - Nairobi distance = 360km
Time taken = 4hrs
Therefore speed = Distance/Time
= 90km/h
The correct answer is A (90km/hr)
6. A motorist crosses a bridge at a speed of 25m/s. What is his speed in km/hr?
1. 80
2. 90
3. 60
4. 30
Working
When working out this kind of question we use a relationship,
If 10 m/s = 36 km/h
25m/s = ?
= ( x 36) km/h
= 90 km/h
The correct answer is B (90km/h)
7. The distance between Mombasa and Mtito Andei is 290km. A bus left Mombasa at 1035h and traveled to Mtito Andei at a speed of 50km/h. At what time did it arrive at Mtito Andei?
1. 1623h
2. 1523h
3. 1423h
4. 1723h
Working
Time = Distance/Speed
= 290/50
= 5 4/5hours or 5h 48min
Arrival time = Departure time = Time taken + Time taken
h       min
10      35
+5     48
16      23
The arrival time 1623 h
The correct answer is A (1623h)
8. Kamau drove from town M to town N a distance of 150 km. He started at 9.30 am and arrived at town N at 11.00 am. He stayed in town for one hour and 50 minutes. He drove back reaching town M at 2.30pm. Calculate Kamau’s average speed for the whole journey.
1. 90km/h
2. 100km/h
3. 60km/h
4. 150 km/h
Working
Total distance from M to N and back
= 150 x 2
= 300 km
Total time taken
From 9.30 - 11.00 = 1 h 30 min
Time spent in town
= 1 h 50 min
Time taken from N to M
= 1430h – 1250h
= 1h 40min
Total time = 5 hours
Average speed = Total distance/Total time taken
=(60km/h)
The correct answer is C (60km/h)
9. The temperature of an object was 20º C below the freezing point. It was warmed until there was a rise of 40º in temperature. What is the reading in the thermometer?
1. 60 Cº
2. 40Cº
3. 20Cº
4. 20Cº
Working
Below freezing point means; - 20
Rose by 40º
Therefore - 20º + 40 = 20 C
The correct answer is C (20º C)