A car of mass 400 kg and travelling at 72 km/h hits a truck of mass 4000 kg and travelling at 9 km/hr in the same direction. The car bounces bact at a speed of 18 km/h. What is the speed of the truck after the impact?

Options

A. 9km/h
B. 18km/h
C. 27km/h
D. 36km/h

Answer

B

Explanation

We will apply the law of conservation of linear momentum.
After collision the mass 2m moves in the N-E direction, with a velocity v'.
For the horizontal direction, `mv + 0 = 2mv'_(x)`
`:. v'_(x) = ( v)/( 2)`
and for the vertical direction ,`mv = 2mv'_(y)`
`:.` The speed of the combined mass in N-E direction is
`v' = sqrt(v'_(x)^(2) + v_(y)^(2))= sqrt(((v)/(2))^(2)+((v)/(2))^(2))`
`= sqrt((v^(2))/( 2)) = ( v)/(sqrt(2))`