The length of a planet's orbit around a star is approximately 17,650,000 km.

It takes the planet about 640 Earth days to complete a full orbit.

What is the planet's average speed in kmh-1 to 3sf?

1150 km/hr

Step-by-step explanation:

Formula for Average Speed is given as = Distance in Kilometers / Time in Hours

In the question we are given the following parameters.

The length of a planet's orbit around a star = Distance = 17,650,000 km.

Time taken to complete a full orbit = 640 Earth days

Step 1

We need to convert the time in days to hours

1 Earth day = 24 hours

640 Earth days =

We cross multiply

640 Earth days * 24 hours

= 15360 hours.

Step 2

Average Speed = Distance in Kilometers / Time in Hours

Average Speed = 17,650,000 km. / 15360 hours

Average Speed = 1149.0885417 km/hr

Approximately to 3 significant figures=

1150 km/hr

Therefore, the planets average speed in kmh-1 to 3sf is 1150 km/hr