Question

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. The total distance covered by the car is: (i) 100 km (ii) 25 km (iii) 15 km (iv) 10 km

Answer 1

Given :-

Case - 1

Speed ( S1) = 40 km/hr

Time (t1 ) = 15 minutes

Case -2

Speed ( S2) = 60 km/hr

Time (t2) = 15 minutes

Required to find :-

• Total distance travelled by the car ?

Formula used :-

$\boxed{\mathrm{\large{ Distance = speed \times time }}}$

Units Conversion :-

Before coming to the Solution it is necessary to convert some units .

So, here we need to convert the time whose values are given in minutes .

But we need those values in hours .

So,

Using the formula

$\boxed{\tt{1 \; Minute = \dfrac{1}{60} hours }}$

So,

1st case :-

Time = 15 minutes

So,

Time in hours = ?

=> 15/60

= 1/4 hours

So, 15 minutes = 1/4 hours

Time = 1/4 hours

Similarly,

2nd case :-

Time period = 15 minutes

From the above we can say that

Time period = 1/4 hours

Solution :-

Given ,

Case - 1

Speed = 40 km/hr

Time = 1/4 hours

So,

Using the formula,

Distance = speed X time

So,

Distance = 40 km/hr x 1/4 hr

Distance (D1) = 10 km

Similarly,

Case - 2

Speed = 60 km/hr

Time = 1/4 hours

Using the same formula,

Distance = speed x time

so,

Distance = 60 km/hr x 1/4 hr

Distance (D2) = 15 km

Hence,

Total Distance = D1 + D2

So,

Total distance = 10 km + 15 km

Total distance = 25 km .

Conclusion :-

Option - ( ii) is correct

Answer 2

Answer:-

Given:-

• Initial speed of car was 40 km h^-1 (v1) and time was 15 mins. (t1)
• Final speed of the car was 60 km h^-1 (v2) and time was 15 mins. (t2).

(i.e. t1 = t2)

To Find:-

Total distance covered (s).

____________...

Formula to be used here:-

s = vt

Case¹ :

v = 40 km h^-1

t = 15 mins.

∴ s = 100/9 m/s × 15 mins.

(Multiply the speed given in km/h with 5/18)

➵ s = 100/9 m/s × 900 s

(1 min. = 60 sec.)

➵ s = 10000 m

➵ s = 10 km (s1)

(1km = 1000m)

Case² :

v = 60 km/h

t = 15 mins.

∴ s = 60 km/h × 15 mins.

➵ s = 50/3 m/s × 900 s

➵ s = 50/3 m × 900

➵ s = 50 m × 300

➵ s = 15000 m

➵ s = 15 km (s2)

Adding (s) of 1st case with 2nd case:-

Total distance covered = s1 + s2

= (10 + 15) km

= 25 km ...(Ans.)

∴ ✔ (ii) 25 km