A movie stunt double is supposed to run across the top of a train (in the opposite direction that the train is moving) and just barely jump off before reaching a tunnel, but after reaching the end of the train (starting from the front). If the train is moving at 150 km/hr, is 2 km long and the tunnel is 20 km away from the end (where the stunt double is going to jump from), how fast (in km/hr) will the stunt double need to run

the required speed/velocity of the stunt double is 13.633 km/h

Explanation:

Given the data in the question;

velocity of train V = 150 km/h

distance = length of train + distance between the tunnel and the end

= 2 km + 20 km = 22 km

first we calculate time t taken by the train to reach the tunnel;

t = distance / velocity

we substitute

t = 22 km / 250 km/h

t = 0.1467 hr

so the velocity of the of the stunt double will be;

velocity = distance / time

we substitute

velocity = 2 km / 0.1467 hr

velocity = 13.633 km/h

Therefore, the required speed/velocity of the stunt double is 13.633 km/h

3. dark matter

empty space could also be a simple vacuum