a truck of mass 2 500 kg travelling at the speed of 20 ms–1 to the right collide head-on with another car of mass 1 000 kg. If both the truck and the car stop after collision, what is the velocity of the car before the collision?​

50 m/s opposite direction to the motion of the truck

Explanation:

From the question,

Applying the law of conservation of momentum

mu+m'u' = V(m+m')...….. Equation 1

Where m = mass of the truck, u = initial velocity of the truck, m' = mass of the car, u' = initial velocity of the car, V = Final velocity after collision

Given: m = 2500 kg, u = 20 m/s, m' = 1000 kg, V = 0 m/s (both car stop after collision)

Substitute these values into equation 1

2500(20)+1000(u') = 0(2500+1000)

2500(20)+1000(u') = 0

Solve for u'

u' = -[2500(20)]/1000

u' = -50 m/s

The negative sign shows that the car travels in opposite direction to the truck

Hence the car initial velocity before collision is 50 m/s in opposite direction to the motion of the truck

d) the number of neutrons plus the number of protons