A bridge that was 8.3 m long has been washed out by the rain several days ago.How fast must a car be going to successfully jump the stream? Although the road is level on both sides of the bridge,the road on the far side is 2.0 m lower than the road on this side.
A) 5.0 m/s
B) 7.8 m/s
C) 13 m/s
D) 25 m/s

Question

Quizplus · Accepted Answer

To successfully jump the stream, the car must attain a speed such that it can travel a horizontal distance of 8.3 m plus the 2.0 m height difference between the roads. Using the conservation of energy, we can equate the gravitational potential energy lost with the kinetic energy gained by the car, i.e.
(mass of car) x g x (height difference) = 0.5 x (mass of car) x (velocity)^2
Solving for velocity, we get velocity = sqrt[(2 x g x height difference)] = sqrt[(2 x 9.81 m/s^2 x 2.0 m)] = 13.0 m/s. Therefore, the best choice is C.

A Bridge That Was 8