Question

Calculate
A car of mass 1000kg has a head-on collision in a 50km/h(30mph) zone with a truck of mass 2500 kg, in
which both vehicles stop dead. If the truck's speed, as
detected by police radar, was 30 km/h, what was the i
car's speed and was the law being broken?(Neglect
the momentum of the truck's load and of the
?
passengers after the collision.)

Answer 1

Answer:

Explanation:

Let us consider the car to be object 1 and the truck to be object 2

then,

mass of car($m_{1}$) = 1000 kg

initial velocity of car($u_{1}$) = ?

final velocity of car($v_{1}$) = 0 km/h

mass of truck($m_{2}$) = 2500 kg

initial velocity of truck($u_{2}$) = 30 km/hr

final velocity of truck($v_{2}$) = 0 km/h

Now by the law

$m_{1}u_{1} + m_{2}u_{2} = m_{1}v_{1} + m_{2}v_{2}\\1000 * u_{1} + 2500*30 = 1000*0 + 2500*0\\1000 * u_{1} + 75000 = 0\\u_{1} = \frac{-75000}{1000} = -75 \ km/hr$

therefore

the speed of car comes out to be 75 km/hr but in the question it is given that the speed is 50 km/hr. therefore as the law cannot be broken the given condition is not possible unless the speed of car is 75 km/hr