Question

A motorist travels for 30 min at a speed of 50 km/h and the next hour at a speed of 65 km/hr. Find his average speed.

Answer 1

Answer:

The average speed is 60 kmph.

Explanation:

Solution :

Case I -

• Speed = 50 kmph
• Time = 30 min
• Distance = ??

★ Speed = Distance/Time

⇒ 50 = Distance/0.5

⇒ 50 × 0.5 = Distance

⇒ 25 = Distance

Distance = 25 km

Case II -

• Speed = 65 kmph
• Time = 1 hour
• Distance = ??

★ Speed = Distance/Time

⇒ 65 = Distance/1

⇒ 65 × 1 = Distance

⇒ 65 = Distance

Distance = 65 km

★ Average speed = Total Distance/Total Time

⇒ (25 + 65)/(0.5 + 1)

⇒ 90/1.5

⇒ 60 kmph

Therefore, the average speed is 60 kmph.

Answer 2

We are given that a motorist travels at 50 km/h for 30 minutes and in the next hour, at 65 km/h. We have to find the average speed of the motorcycle or the motorist.

We know,

Average speed is obtained by dividing total distance travelled by total time taken.

Finding total distance travelled:- (S1 + S2)

We also know,

S = vt

S1 = (50 km/h)(½ h)

= 25 km

S2 = (65 km/h)(1 h)

= 65 km

Hence,

Total distance = S1 + S1

or, 25 km + 65 km

or, 90 km

NOW,

Finding average speed:-

(See formula)

(90 km)/(1½ h)

→ (90 km)/(3/2 h)

→ (90 × 2 km)/(3 h)

→ (30 × 2 km)/(h)

→ 60 km/h Ans.