CAIE A-Level Physics 2.1.7 Uniformly Accelerated Straight-Line Motion

Practise selecting constant-acceleration equations for motion and free fall, using signs, units, initial conditions, roots and physical feasibility.

Exam points

Select and apply the appropriate uniformly accelerated-motion equation to solve for displacement, velocity, time or acceleration.
Solve vertical free-fall problems using g and the correct sign convention, neglecting air resistance.
Check the roots, units, initial conditions and physical feasibility of the result.

[Maximum number: 2]

A delivery company suggests using a remote-controlled aircraft to drop a parcel into the garden of a customer. When the aircraft is vertically above point P on the ground, it releases the parcel with a velocity that is horizontal and of magnitude $5.4 \mathrm{~ms}^{-1}$ . The path of the parcel is shown in Fig. 2.1.

Fig. 2.1 (not to scale)

The parcel takes a time of 0.81 s after its release to reach point Q on the horizontal ground. Assume air resistance is negligible.

Determine the height h of the parcel above the ground when it is released.

$\begin{aligned} s=u t+1 / 2 a t^{2} h=1 / 2 \times 9.81 \times 0.81^{2} \end{aligned}$

C1

$=3.2 \mathrm{~m}$

A1

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2.1.7—Equations that represent uniformly accelerated motion in a straight line question 1