An 800 kg car moving at 80 km hr\(^{-1}\) collides with a 1200 kg car moving at 40 km hr\(^{-1}\) in the same direction. If the cars stick together, calculate their common velocity.
60 km hr\(^{-1}\)
8 km hr\(^{-1}\)
40 km hr\(^{-1}\)
56 km hr\(^{-1}\)
Explanation
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Discussions (14)
The two cars are moving in the same direction, hence their initial momenta will be both positive and thus added, not subtracted as shown in the explanation.
(800 x 80) + (1200 x 40)
= (800 + 1200) V
= 64000 + 48000 = 2000V
112000 = 2000V
V = 112000/2000
= 56kmh−1
The common velocity = 56kmhr−1
Hence the correct answer is D, not A
The two cars collide, and stick, which means, it is an inelastic collison which is characterized with common velocity
From conservation,
Initial momentum= final momentum
M1U1 + M2U2 = V(M1+M2)
V= (M1U1+M2U2)/(M1+M2)
=(800×80 + 1200×40)/(800+1200)
=(64000+48000)/2000
=112000/2000
V=56kmh-¹ or 56km/h
My school that option isn't A
It's D
Collision B4 impact= collision after impact
800*80+1200*40=800+1200(v)
V=56km/hr
y'all wrong my school is right. if u make reference to ur relative velocities u did understand that velocities in opposite directions are being added while velocities in same directions are subtracted. no cap check ur text books or browse 'em.
Yes, the balls are moving in the same direction but the first ball has less mass and more speed and the second ball has more mass and less speed. Therefore, it is moving slower than the first ball.
The first ball caught up to it and collided with it, they are now stuck and moving together in the same direction.
When two objects are moving in the same direction, their relative velocity is the difference in their velocities, we subtract. For example, if one train is moving west at 40 km/h and another is moving west at 20 km/h, the relative speed between the two trains is 20 km/h because they are in the same directions, we subtract.
In contrast, if two objects are moving in opposite directions, their relative velocity is the sum of their velocities.
Hence what the question was asking. Hope the confusion is cleared.
Guys my school is actually correct because it's in the same direction that means it caught up to the other ball not that they collided and balls moving in the same direction will be subtracted
