Question 1
1
Question 1(b)
1(b)
Under certain conditions, the distance s moved in a straight line by an object in time t is given by where a is the acceleration of the object. State two conditions under which the above expression applies to the motion of the object. 1 2
Answer
initial speed / velocity is zero B1 (non-zero magnitude of) acceleration is constant / uniform (and in a straight line) B1
Question 1(c)
1(c)
The variation with time t of the velocity v of a car that is moving in a straight line is shown in Fig. 1.1.
Question 1(c)(i)
1(c)(i)
Compare, qualitatively, the acceleration of the car at time \(t=8.0 \mathrm{~s}\) and at time \(t=14.0 \mathrm{~s}\) in terms of: - magnitude - direction.
Answer
magnitude of acceleration at \(t=8.0 \mathrm{~s}\) is less than that at \(t=14.0 \mathrm{~s}\) B1 - direction of acceleration at \(t=8.0 \mathrm{~s}\) is opposite to that at \(t=14.0 \mathrm{~s}\) B1
Question 1(c)(ii)
1(c)(ii)
Determine the magnitude of the acceleration of the car at time \(t=4.0 \mathrm{~s}\). acceleration = \(\mathrm{ms}^{-2}\)
Answer
a= gradient or a=(v-u) / t or \(a=\Delta v /(\Delta) t\) C1 \[ \begin{aligned} a=\text { e.g. }(20+10) / 12 \text { or }(0+10) / 4 \text { or }(20-0) /(12-4) a=2.5 \mathrm{~m} \mathrm{~s}^{-2} \end{aligned} \] A1
Question 1(c)(iii)
1(c)(iii)
The car is at point X at time t=0. Determine the magnitude of the displacement of the car from X at time \(t=12.0 \mathrm{~s}\). displacement = m
Answer
\[ \text { displacement }=[1 / 2 \times(12-4) \times 20]-[1 / 2 \times 4 \times 10] \] or displacement \(=(-10 \times 12)+\left(1 / 2 \times 2.5 \times 12^{2}\right)\) or displacement \(=(20 \times 12)-\left(\frac{1}{2} \times 2.5 \times 12^{2}\right)\) or displacement \(=1 / 2 \times(20-10) \times 12\) C1 displacement \(=60 \mathrm{~m}\) A1