​A rally car is at the start line for a race. Marker posts are placed every 20 metres.



The time taken for the rally car to reach the last marker post is 5 seconds.

(a)​Calculate the average speed of the car between the first and last marker post. (3)

(b) ​A spectator decides to calculate the instantaneous speed of the car using the last marker post.
Describe how the instantaneous speed of the race car could be measured as it passes the last marker post.

Your description must include:

• measurements made
• any necessary calculations​​​​​​​​ (3)