Physics; Momentum,?

Question

Two wagons, each of unloaded mass 1000kg, are free to travel on a straight horizontal track. One of the wagons carries a load of mass 'm'kg and the other is empty. the empty wagon is travelling at 5ms-1 when it runs into the loaded wagon which is stationary. immediately after the collision the empty wagon continues in the same direction with speed 0.5 ms-1, and the loaded wagon starts to move with speed 1.5ms-1. Find the value of 'm' ?

Answer 1

This is a conservation of momentum problem solved in the following way

momentum = mass * velocity

momentum of unloaded wagon = 1000 *5 = 5000 kg m^-1

momemtum of unloaded wagon after collision = 1000 * 0.5 = 500 kg m^-1

so the momentum of the loaded wagon after the collision = 5000-500 = 4500 kg m^-1

now this means that 4500 = (m+1000) * 1.5

therefore 3000 = m +1000
and m= 2000 kg

Answer 2

Newton's 2nd law i think - whatever hits something, that something carries on travelling with the proportional amount of force...(or something like that, I can't remember precisely what it was)

2 wagons each weigh 1000 kg
first one (empty) travelling at 5m/s

2nd one travels at 0.5m/s after being hit but has mass m (let total mass of this wagon be x)

mass*speed must be equivalent for both wagons in order to apply to Newton's law

thus...
1000kg*5m/s=x*0.5m/s
5000=0.5x

thus x = 10000kg

since the original second wagon was 1000kg unloaded

x-1000=m
m=9000kg

wow, 9000kg for a bloody wagon. Is this even possible?

Answer 3

total momentum before and after collision is constant so :
p(initial)=(m+1000)(0) + (1000) (5)= 5000
that m+1000is mass of stationary wagon and 0 is its velocity and 1000 is mass of 2nd one and 5 is its speed.
p(final) i.e after collision is
p(final)=1.5(m+1000) + 0.5(1000)
we have p(initial)=p(final) so :
5000=1.5m+1500+500
then 5000=1.5m + 2000 and
m= 3000/1.5 that is 2000 Kg

Answer 4

You should have studied more in class, rather than posting your homework here ;-)