**Question 5**:

The
diagram above shows the speed-time graph of a moving object for 15 seconds. Find

**(a)**

**the speed of the object at**

*t*= 9s.

**(b)**the distance travel by the object for the first 12 seconds.

*Solution:***(a)**

The
speed of the object at

*t*= 9s is**6 ms**^{-1}**(b)**

= Area under the speed-time graph

= Area of triangle

= ½ × 12 × 8

=

**48 m****Question 6**:

The
diagram above shows the speed-time graph of a moving object for 15 seconds.

**(a)**Find the time interval when the object moves with constant speed.

**(b)**Find the acceleration from

*t*= 6s to

*t*= 12s.

**(c)**State the time when the object is stationary.

*Solution:***(a)**

Time
interval when the object moves with constant speed

= 12
– 6

=

**6 s**

**(b)**

**(c)**

Time
when the object is stationary is at

**15s**.