Day 76: Energy and Momentum Practicum



We did this today in AP Physics C.

The scenario: A cart with a pre-compressed spring travels towards a stationary cart. Upon impact, the spring uncompress and the two carts move away from each other.

The known quantities: The masses of the carts. The pre- and post-impact velocities of just the spring loaded cart as determined by the motion detector.

The challenge: Determine the energy stored in the spring.

The check: Measure the velocity of the spring cart when the spring is used to launch the cart from rest.

(Variation: Given the the compression of the spring, determine the spring constant of the launcher. Check by compressing the launcher with a push/pull spring scale.)

Students must use both momentum and energy conservation to correctly solve this challenge.

CREDIT: Based upon an idea from John Clement’s recent post to the Modeling listserv, in which he envisions a collision which ADDS kinetic energy to the system.


About Frank Noschese

HS Physics Teacher constantly questioning my teaching.

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