Question

A van is traveling on a road at a speed of 55 km/h. A girl sitting near the driver of the van throws a paper airplane to a boy at the back of the van with a speed of 2 km/h.
The speed of the paper airplane, to the nearest whole number relative to a stationary observer on the side of the road, is ___ km/h.

Answer 1

Answer:

53 km/h

Explanation:

Let's take as positive direction the direction in which the van is moving. In this case, we can write as follows:

- Velocity of the van relative to the road: $v_v = 55 km/h$

- Velocity of the paper airplane relative to the van: $v_a = -2 km/h$ (with a negative sign since it is moving into opposite direction)

Therefore, the velocity of the paper airplane relative to the road (stationary observer) will be

$v=v_v + v_a = 55 km/h - 2 km/h = 53 km/h$

Answer 2

A van is traveling on a road at a speed of 55 km/h relative to a
stationary observer on the side of the road. A girl sitting near the
driver of the van throws a paper airplane to a boy at the back of the
van with a speed of 2 km/h relative to the girl, the boy, and the van.

The speed of the paper airplane, relative to the same stationary observer
on the side of the road, is (55 - 2) = 53 km/h.  No rounding is necessary.