## Question 3:

### Part (a):
| Answer/Working | Mark | Guidance |
|---|---|---|
| $7^2 = 2 \times 9.8h$ | M1 | Use of $v^2 = u^2 + 2as$ with $u=0, v=7$, or alternative complete method to find $h$ |
| $h = 2.5$ | A1 | Condone $h = -2.5$ in working but final answer must be positive |

### Part (b):
| Answer/Working | Mark | Guidance |
|---|---|---|
| $9 \times 7 = 10.5\, u$ | M1 | Use CLM to find speed of blocks after impact. Condone additional factor of $g$ throughout. |
| $u = 6$ | A1 | |
| $0^2 = 6^2 - 2a \times 0.12$ | M1 | Use of $v^2 = u^2 + 2as$ with $u=6, v=0$. Allow for their $u$ and $v=0$. Allow for $u=7, v=0$. Accept alternative suvat method to form equation in $a$. Condone use of 12 for 0.12 |
| Correctly substituted equation in $a$ with $u=6, s=0.12$ (implied by $a=150$) | A1 | |
| $(\downarrow)\; 10.5g - R = 10.5 \times (-a)$ | M1 | Use of $F=ma$ with their $a \neq \pm g$. Must have all 3 terms and 10.5. Condone sign error(s) |
| $(\downarrow)\; 10.5g - R = 10.5 \times (-150)$ | A1 | Unsimplified equation with $a$ substituted and at most one error (their $a$ with wrong sign is 1 error) |
| Correct unsimplified equation with $a$ substituted | A1 | |
| $R = 1680$ or $1700$ | A1 | |

**Alternative for last 6 marks:**
| Answer/Working | Mark | Guidance |
|---|---|---|
| $\frac{1}{2} \times 10.5 \times 6^2 + 10.5 \times 9.8 \times 0.12 = R \times 0.12$ | M2 | Energy equation (needs all three terms) |
| | A3 | $-1$ each error; A1A1A0 for 1 error, A1A0A0 for 2 errors |
| $R = 1680$ or $1700$ | A1 | |

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