Collisions Flashcards

All 4 cards in this deck

What are the steps to find the velocity of two objects that move off together after a collision?

e.g. a 2 kg trolley at 3 m/s hits a stationary 4 kg trolley

1. Total momentum before: $2 \times 3 + 0 = 6$ kg m/s
2. Momentum after = 6 kg m/s, combined mass $= 2 + 4 = 6$ kg
3. $v = 6 \div 6 = 1$ m/s

What are the steps to find the velocity of a piece after an explosion or push-apart?

e.g. a stationary pair of trolleys spring apart; the 2 kg trolley moves right at 1 m/s, the other has mass 1 kg

1. Total momentum before $= 0$
2. Momentum after $= 0$: $(2 \times 1) + (1 \times v) = 0$
3. $v = -2$ m/s, i.e. 2 m/s to the left

True or false? When two objects moving in opposite directions collide, you add their momenta as two positive numbers.

False. One momentum must be taken as negative, so the total is the difference.

True or false? When two objects collide and move off together, you divide the total momentum by the combined mass to get their velocity.

True. The two objects now move as one object of mass $m_1 + m_2$.