Question

A bicyclist in the Tour de France crests a mountain pass as he moves at 15 km/h. At the bottom, 4.2 km farther, his speed is 65 km/h. Estimate his average acceleration while riding down the mountain.

Answer 1

18 km/hr*1000m/km*1 hr/3600 sec= 5 m/sec 

85 km/hr= 23.6 m/s 

distance = 4000m 

distance= initial distance+initial velocity*time+ 1/2 acceleration*time^2 

initial distance=0 

4000= 5.0*t+ 1/2 (accel)(time)^2 

Velocity=initial velocity+ acceleration * time 

23.6 m/s= 5.0 m/s+ acceleration * time 

We now have two equations and two unknowns. Solve them and you have your answer.