What type of device is a car engine?
a. a heat pump that uses heat to do work
b. a heat engine that uses work to move heat
c. a heat pump that uses work to move heat
d. a heat engine that uses heat to do work

D A heat engine that uses heat to do work

can be answered using momentum.

momentum = p

p1= mass1 * velocity1

p1 = p2

therefore

p1 = 6kg * 4m/s

p1 = 24kgm/s

p2=m2 * v2

24 kgm/s = 7kg * v2

v2 = 24 kgm/s / 7kg

v2= 3.42 m/s

f is prop to m1xm2 double m1 double force