Question

A car with a mass of 800 kg, moving at +15 m/s, crashes head on with a 1500 kg truck moving at -45.5 m/s in the opposite direction. If the two cars become intertwined, with what velocity does the wreckage move?

Answer 1

Answer:

v = -24.5 m/s

Explanation:

Use conservation of momentum P = m*v. Unless there are external forces involved, total momentum must be conserved.

P: momentum

m: mass

v: velocity

1. calculate the total momentum before the collision:

$P=m_{car}v_{car} + m_{truck}v_{truck}$

2. the total momentum after the collision must not change:

$P_{before}=P_{after}$

3. after the collision the velocity of the car is the same as the velocity of the truck:

$v = v_{car} = v_{truck}$

4. combining 2. and 3.:

$P= (m_{car}+m_{truck})v$

5. this equation only has one unknown and can be solved for v:

$v = \frac{P}{m_{car}+m_{truck}} =\frac{m_{car}v_{car} + m_{truck}v_{truck}}{m_{car}+m_{truck}}$

$v=\frac{800*15 + 1500 * (-45.5)}{800 + 1500} = -24.5$