Why is water cooler then sand at the beach

This is because large specific heat of water as compared to the specific heat of sand. due to large specific heat , it take water longer to heat Up  and cool down. on the other hand, the sand has smaller specific heat , and hence heats up or cools down faster. So on a hot day , the sand on the beach , heats up quickly while the water heats up slowly. hence the water is cooler as compared to sand at the beach.

terd muffin is the correct answer

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