1 · IGCSE Physics
Momentum in collisions
Set the masses and velocities of two trolleys, choose whether they stick or bounce, and compare momentum and kinetic energy before and after the collision. Velocities to the right are positive.
p = m v
mAuA + mBuB = mAvA + mBvB
Ek = ½ m v²
F = Δp / Δt
mAuA + mBuB = mAvA + mBvB
Ek = ½ m v²
F = Δp / Δt
| Before | After | |
|---|---|---|
| vA / m s⁻¹ | ||
| vB / m s⁻¹ | ||
| Total p / kg m s⁻¹ | ||
| Total Ek / J |
Try this
- Set equal masses, uA = 2.0 m s⁻¹, uB = 0 and choose elastic: what happens to each trolley's velocity?
- Choose “Stick together” and change the masses: check that total momentum stays the same but kinetic energy always falls.
- Keep everything fixed and halve the contact time: how does the force on B change, and why do crumple zones make collisions longer?
Exam tip: choose a positive direction first and give velocities to the left a negative sign, otherwise your momentum totals will not balance.