Answering Numeric Linear Motion Problems Write a column containing each of the quantities u, v, a, s and t, filling in the quantities you’re given (usually you’ll be given three in the question). Use the equations of motion to calculate the unknown quantities. All quantities should be put in their SI units.
Memory Aid: It may help to refer to these as ‘uvast’ questions, at this will help remind you of the five quantities we deal with in linear motion.
SAMPLE PROBLEM 2I
A body starting from rest accelerates uniformly to a velocity of 60 m s1 due south. After 10 s calculate its: (i) acceleration
(ii) displacement SAMPLE ANSWER 2I
Fill in the values given for u, v, a, s and t in their standard units: u 0 m s1 v 60 m s1 a s t 10 s When we know three of our uvast quantities,we can calculate the other two using the equations of motion. Ask yourself:‘Which equation relates the three quantities I know with the one I’m trying to find?’ (i) Calculating its acceleration: v u at
(ii) Calculating its displacement: Fill in the values given:
The body is accelerating at 6 m s2. (60) (0) a(10)Qa 60
10 6
s ut 1 2 at2
Fill in the values given:
s (0)(10) 1 2 (6)(10)2Qs 600
2 300
The displacement of the body is 300 m s2 due south. Alternatively we could have used the equation: v2 u2 2as Fill in the values given:
The displacement of the body is 300 m due south. (60)2 (0)2 2(6)s Qs 3 600
12 300 SAMPLE PROBLEM 2J
A race car travelling at 144 km h1 decelerates uniformly to a velocity of 36 km h1 over a distance of 75 m. What is the deceleration of the race car?
