Question

A car of mass 800kg collides with a truck of mass 5000kg traveling at 40m/s.The car is thrown on to bonet of the truck which continous to more after impact at 10m/s in the original direction .How fast was the car moving.

Answer 1

177.5 m/s (*)

Explanation:

Applying the conservation of momentum for elastic collisions, with:

m1 = mass of car: 800 kg

v1 = velocity of car (unknown)

m2= mass of truck: 5000 kg

v2 = velocity of truck -40 m/s (opposite direction with car)

v2' = velocity of truck after collision = -10m/s (opposite direction with car)

=> m1 x v1 + m2 x v2 = (m1 + m2)v2'

=> 800 x v1 + 5000 x (-40) = (800 + 5000) x (-10)

<=>800 x v1 = 200000 - 58000

<=> 800 x v1 =142000

<=> v1 = 177.5 m/s

This result looks like unreal.

In fact, it would be more reasonable if the velocities of truck before and after collision are 40km/h and 10km/h respectively. Hence, the result is 177.5 km/h.

Hope this helps!