Question

A bus moves with a speed of 80km/h for 15 minutes and then with a speed of 60km/h for the next 15 minutes. The total distance covered by the car is- (a)100km (b)50km (c) 35km (d)70km

Answer 1

Correct Question

A bus moves with a speed of 80km/h for 15 minutes and then with a speed of 60km/h for the next 15 minutes. The total distance covered by the bus is-

(a)100km (b)50km (c) 35km (d)70km

Solution-

Let us assume the the distance covered by the bus is "x" km.

Case 1)

A bus moves with a speed of 80km/h for 15 minutes.

Here; speed = 80 km/hr and time = 15 min = 0.25 hr.

We know that,

Distance = Speed × Time

Substitute the known values,

→ x = 80 × 0.25

→ x = 20 km

So, the distance covered by the bus in first half is 20 km.

Case 2)

The bus cover next 15 minutes with a speed of 60 km/hr.

Again,

Distance = Speed × Time

→ x = 60 × 0.25

→ x = 15 km

Total distance covered by the bus = Distance covered by the bus in (first 15 minutes + next 15 minutes)

= (20 + 15) km

= 35 km

Therefore, the total distance covered by the bus is 35 km.

Option (c) 35 km

Answer 2

Given:

Speed of bus for first 15 min, S₁= 80 km/h

Speed of bus for last 15 min, S₂= 60 km/h

To Find:

The total distance covered by the bus

Solution:

We know that,

• $\pink{\boxed{\bf{Distance=Speed\times Time}}}$

$\rule{190}{1}$

15 minutes can also be expressed as

$\longrightarrow\rm{15\ min=\dfrac{15}{60}\ h=\dfrac{1}{4}\ h}$

Let t₁ be the time taken by bus to travel with speed 80 km/h and t₂ be the time taken by bus to travel with speed 60 km/h

Here

$\longrightarrow\rm{t_{1}=t_{2}=\dfrac{1}{4}\ h}$

$\rule{190}{1}$

Now,

Let D₁ be the distance covered in first 15 minutes and D₂ be the distance covered in last 15 minutes

So,

$\longrightarrow\rm{D_{1}=S_{1}\times t_{1}}$

$\longrightarrow\rm{D_{1}=80\times \dfrac{1}{4}}$

$\longrightarrow\rm{D_{1}=20\ km}$

Also,

$\longrightarrow\rm{D_{2}=S_{2}\times t_{2}}$

$\longrightarrow\rm{D_{2}=60\times \dfrac{1}{4}}$

$\longrightarrow\rm{D_{2}=15\ km}$

$\rule{190}{1}$

Now,

Let D be the total distance covered by bus

So,

$\longrightarrow\rm{D=D_{1}+D_{2}}$

$\longrightarrow\rm{D=20+15}$

$\longrightarrow\rm\green{D=35\ km}$

Hence, the correct option is (c)