car with a mass of 50 Kg and velocity of 20 m/s collided with a truck of a velocity of 60 m/s, if the momentum is conserved what is the mass of the truck?

Will you chech and finish these for me, because i am stumped with them.

When you jump from an elevated position you usually bend your knees upon reaching the ground. by doing this, you make the time of the impact about 10 times as great as for a stiff-legged landing. in this way the average force your body experiences is a) less than 1/10 as great. b) more than 1/10 as great. c) about 1/10 as great.d) about 10 times as great.

An architect plans to use solar energy to heat the next house he designs. what principle of absorption and infrared energy can be applied to the design of the new house? how could she apply to those principals?