Answer:
45 km/h
Explanation:
The kinetic energy of the car is given by:
[tex]K=\frac{1}{2}mv^2[/tex]
where
m=1000.0 kg is the mass of the car
v=15 km/h is its speed
The kinetic energy of the truck is given by:
[tex]K'=\frac{1}{2}MV^2[/tex]
where
M = 2000.0 kg is the mass of the truck
V is its unknown speed
We know that the truck has 18 times the kinetic energy of the car, therefore:
[tex]K'=18 K[/tex]
Substituting and re-arranging, we can find V:
[tex]\frac{1}{2}MV^2 = 18 \cdot \frac{1}{2}mv^2\\V=\sqrt{\frac{18 mv^2}{M}}=\sqrt{\frac{18(1000.0 kg)(15 km/h)^2}{(2000.0 kg)}}=45 km/h[/tex]
