Conservation of Mechanical Energy

How the real exam tests it

Questions from real CSCA papers that test this concept. Work each one out before you open the answer.

1. CSCA Physics December 2025 Past Paper
   Question: A basketball with mass $\mathrm { m } = 0.5 \mathrm {~kg}$ bounces from the ground to a height $\mathrm { h } = 1 \mathrm {~m}$ before falling back to the ground. The change in gravitational potential energy during this entire process is ( ). $\left( \mathrm { g } = 10 \mathrm {~m} / \mathrm { s } ^ { 2 } \right)$
   • A．10 J
   • B．0.5 J
   • C．5 J
   • D．0 J
   Show answer & solution

   Answer: D

   1 Initial and final positions are both on the ground, so gravitational potential energy change over the whole bounce cycle is $\Delta \mathrm { U } = 0$. 2 Therefore the net change in gravitational potential energy is 0 J .
   See it in the full CSCA Physics December 2025 Past Paper
2. CSCA Physics March 2026 Past Paper
   Mass $m$ is thrown upward at v from ground level, no air resistance. Mechanical energy at the highest point is (ground $=$ zero PE)
   • A．$\frac { 1 } { 2 } m v ^ { 2 }$
   • B．mgh
   • C．$1 / 2 m v ^ { 2 } + m g h$
   • D．0
   Show answer & solution

   Answer: A

   No air resistance → mechanical energy conserved. At launch: $\mathrm { E } = 1 / 2 \mathrm { mv } ^ { 2 } + 0 = 1 / 2 \mathrm { mv } ^ { 2 }$. At top: $\mathrm { KE } = 0$, $\mathrm { PE } = \mathrm { mgh }$, but total E still $= 1 / 2 \mathrm { mv } ^ { 2 }$. B and C are not correct expressions; D is clearly wrong. Answer: A．
   Take the full CSCA Physics March 2026 Past Paper — timed & graded
3. CSCA Physics April 2026 Past Paper
   A 0.2 kg ball falls freely from a height of 2 m to the ground. The change in its gravitational potential energy is $\left( g = 10 \mathrm {~m} / \mathrm { s } ^ { 2 } \right)$
   • A．0 J
   • B．- 4 J
   • C．4 J
   • D．2 J
   Show answer & solution

   Answer: B

   As the ball descends, its gravitational PE decreases. $\Delta E _ { p } = - m g h = - 0.2 \times 10 \times 2 = - 4 \mathrm {~J}$.
   Take the full CSCA Physics April 2026 Past Paper — timed & graded