For the first hour a car is driven at a constant speed of 90 km/hr. The motor begins to vibrate and the driver reduces the speed to 45 km/hr for another 2 hours. The average speed for the entire trip is
A) 90.0 km/hr.
B) 25.5 km/hr.
C) 60.0 km/hr.
D) 67.5 km/hr.
E) 45.0 km/hr.

Question

Quizplus · Accepted Answer

To find the average speed of the entire trip, we need to use the formula:

average speed = total distance ÷ total time

Let's first find the total distance traveled.

Distance traveled in the first hour at 90 km/hr = 90 km
Distance traveled in the next 2 hours at 45 km/hr = 2 x 45 km = 90 km

Total distance traveled = 90 km + 90 km = 180 km

Now, let's find the total time taken.

Time taken in the first hour at 90 km/hr = 1 hour
Time taken in the next 2 hours at 45 km/hr = 2 hours

Total time taken = 1 hour + 2 hours = 3 hours

Using the formula:

average speed = total distance ÷ total time

We get:

average speed = 180 km ÷ 3 hours
average speed = 60 km/hr

Therefore, the average speed for the entire trip is 60 km/hr, which is closest to choice C).

For the First Hour a Car Is Driven at a Constant