Define the term momentum.
A child is standing on a scooter on level ground. The total mass of the child together with the scooter is $16\,\text{kg}$. Starting from rest, the child gives one push on the ground with her foot, causing acceleration. The push continues for $1.1\,\text{s}$. Once the push ends, the child and scooter move at $0.60\,\text{m s}^{-1}$. Work out the average resultant horizontal force acting on the child and the scooter during the push.
Later on, the child in (b) moves downhill on a slope that makes a constant angle to the horizontal, as shown in Fig. 2.1. At point $A$ her speed is $0.60\,\text{m s}^{-1}$. She has a constant acceleration of $0.85\,\text{m s}^{-2}$ parallel to the slope. After $3.7\,\text{s}$, she arrives at point $B$. Calculate the distance $x$ travelled by the child along the slope from $A$ to $B$.
At point $B$, the child in (c) uses the brake with a constant force so that the velocity stays constant. Point $C$ is $18\,\text{m}$ from point $B$, as shown in Fig. 2.2. The work done by the braking force from $B$ to $C$ is $250\,\text{J}$. Determine the magnitude of the braking force.
On Fig. 2.3, sketch how the kinetic energy of the child and scooter changes with distance travelled from point $A$ to point $C$. You do not need to include numerical kinetic energy values.