Question

km/minute
m/minute
km/hour
m/second
D. Answer the following questions in brief.
A boy walks to his school with a constant speed of 4 km/h and reaches there in
30 minutes. Find the distance of the school from his house.
The distance between two stations is 216 km. A bus takes 4 hours to cover this
distance. Calculate the average speed of the bus in km/hour.
1.
2.
3. Two Cars, A and B, (starting, at the same time, from the same point) are moving
with average speeds of 40 km/h and 50 km/h, respectively, in the same direction.
Find how far will Car B be from Car A after 3 hours.
4.
A car moves with a speed of 40 km/h for 15 minutes and then with a speed of
60 km/h for the next 15 minutes. Find the total distance covered by the car in
these 30 minutes.
5.
Define the term “Periodic motion! Give two examples of periodic motions that
can be used to measure time.
97

Answer 1

Explanation:

Speed = 4 km/h

Time = 30 mins

Distance = speed * time = 4 km/h * 1/2 (because 30 mins is half of an hour)

= 2km

Ans) The distance of his house to his school is 2 km.

Time = 4 hrs

Distance = 216 km

Speed = distance / time = 216 / 4 = 54 km/h

Ans) The speed of bus is 54 km/h.

Car A:

Speed = 40 km/h

Time = 3hrs

Distance = speed * time = 40 * 3 = 120 km

Car B:

Speed = 50 km/h

Time = 3hrs

Distance = 50 * 3 = 150 km

Distance between Car A and Car B = 150 - 120 = 30 km

Ans) Car B is 30km far from Car A after 3 hours

Speed = 40km/h

Time = 15 mins = 1/4 of an hour

Distance = 40km/h * 1/4 = 10 km

Speed = 60km/h

Time = 15 mins = 1/4

Distance = 60km/h * 1/4 = 15km

Total distance = distance1 + distance2 = 10 + 15 = 25km

Ans) The total distance of car is 25km.

When an object repeats it's motion cycle after a fixed interval of time, the type of motion is periodic motion. Examples = orbit of the Earth around sun,

the hands of a clock.