Constant Acceleration Question 1

Question: a car accelerates uniformly from 5.0 m s^-1 to 25 m s^-1 over a distance of 100 m. Calculate (a) its acceleration and (b) the time taken.Step 1: list the suvat quantities. Write down what you know and what you want.s = 100 m, u = 5.0 m s^-1, v = 25 m s^-1, a = ?, t = ?Step 2: choose the formula. For part (a), t is not known, so use the formula without t:v² = u² + 2as25² = 5.0² + (2 × a × 100)625 = 25 + 200aa = 600 ÷ 200 = 3.0 m s^-2Step 3: part (b). Now that a is known, use v = u + at:t = (v - u) ÷ a = (25 - 5.0) ÷ 3.0 = 6.7 sCheck: s = ½(u + v)t = ½(5.0 + 25) × 6.67 = 100 m, which matches the distance given.Tips: always write out s, u, v, a and t first. Pick the formula that leaves out the quantity you neither know nor need. Keep the unrounded value (6.67 s) for any later working, and give final answers to the same number of significant figures as the data.