**Challenging Question 2**:

Zulkifli starts driving his car from home with a constant acceleration and reaches a velocity of 30 m/s in 6.0 seconds. Find

- the acceleration of Zulkifli's car.
- the displacement of Zulkifli's car 5.0 seconds after it started moving.
- the displacement of Zulkifli's car in the fifth second..
- velocity of Zulkifli's car at time t = 4.0 seconds?
- velocity of Zulkifli's car after moving 30.0 meters from the starting point.

**Answer**:

It's advisable to list down all the information that we have.

Initial velocity, u = 0 (Start driving from his home)

Final velocity, v = 30 ms

^{-1}

Time taken, t = 6s

a. Acceleration, a = ?

$$\begin{array}{l}\left(30\right)=(0)+a(6)\\ 6a=30\\ a=\frac{30}{6}=5m{s}^{-2}\end{array}$$

b. t = 5s, s = ?

$$\begin{array}{l}s=ut+\frac{1}{2}a{t}^{2}\\ s=(0)(5)+\frac{1}{2}(5){(}^{5}\\ s=62.5m\end{array}$$

(Note: We can't use v=30 for this calculation because it is the final velocity at 6s, but not 5s)

c. Fifth second is a period from 4s to 5s.

Displacement after 4s,

$$\begin{array}{l}s=ut+\frac{1}{2}a{t}^{2}\\ s=(0)(4)+\frac{1}{2}(5){(}^{4}\\ s=40m\end{array}$$

Displacement in the fifth second

= 62.5m - 40m = 22.5m

d. t = 4s, v = ?

$$\begin{array}{l}v=u+at\\ v=(0)+(5)(4)=20m{s}^{-2}\end{array}$$

e. s = 30.0m, v = ? $$\begin{array}{l}{v}^{2}={u}^{2}+2as\\ {v}^{2}={(}^{0}+2(5)(30)\\ {v}^{2}=300\\ v=\sqrt{300}=17.3m{s}^{-1}\end{array}$$

### Reference

$$\begin{array}{l}v=u+at\\ s=ut+\frac{1}{2}a{t}^{2}\\ {v}^{2}={u}^{2}+2as\\ s=\frac{1}{2}(u+v)t\end{array}$$