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Two air-track carts move toward one another on an air track. Cart 1 has a mass of 0.35kg and a speed of 1.2m/s.Cart 2 has a mass of 0.61kg. What speed must cart 2 have if the total momentum of the system is to be zero? Since the momentum of the system is zero. does it follow that the kinetic enery of the system is alos zero?

my answer: momentum=mass x velocity
.35 x 1.2= .42 so .61 x ?= 0.42
0 .69 is the speed of cart 2

kinetic energy= 1/2mass x velocity so
1/2(.61) x .69= 0.21

Am I doing this correctly?

2007-03-13 08:08:34 · 2 answers · asked by christy r 1 in Science & Mathematics Physics

2 answers

pretty much !! however for the momentum to be zero for the system, make sure you indicate the direction of the velocity of one of the carts as being negative from the other.

as far as kinetic energy goes. No, because energy doesn't have a vector (direction) it only has magnitude. whereas momentum is a vector (speed and direction).
So you can't have a zero kinetic energy system based on the carts. unless they both are not moving.

Do your research, check my facts on the difference between a vector and a magnitude. You'll learn the difference.

2007-03-13 08:19:17 · answer #1 · answered by a1tommyL 5 · 0 0

You calculated correctly the speed of the cart 2. To specify the velocity, you need to also specify the direction that cart 2 is traveling, which will be opposite that of cart 1 in order for the sum of momentums to be zero.

Kinetic energy is not zero just because momentum is zero. Your formula for kinetic energy is incorrect. Kinetic energy is proportional to the square of velocity.

KE=0.5 * mass * velocity^2

2007-03-13 08:27:19 · answer #2 · answered by Elisa 4 · 1 0

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