Question Number 59780 by necx1 last updated on 14/May/19
$${An}\:{earth}-{based}\:{observer}\:{sees}\:{rocket}\:{A} \\ $$$${moving}\:{at}\:\mathrm{0}.\mathrm{70}{c}\:{directly}\:{towards}\:{rocket} \\ $$$${B},{which}\:{is}\:{moving}\:{towards}\:{A}\:{at}\:\mathrm{0}.\mathrm{80}{c}. \\ $$$${How}\:{fast}\:{does}\:{rocket}\:{A}\:{sees}\:{rocket}\:{B} \\ $$$${approaching}? \\ $$$$ \\ $$
Answered by ajfour last updated on 14/May/19
$$\mathrm{v}_{\mathrm{rel}} =\:\frac{\mathrm{0}.\mathrm{7c}+\mathrm{0}.\mathrm{8c}}{\mathrm{1}+\mathrm{0}.\mathrm{56}}\:\approx\:\mathrm{0}.\mathrm{9615c} \\ $$