Answer:
Final velocity = 7.677 m/s
KE before crash = 202300 J
KE after crash = 182,702.62 J
Explanation:
We are given;
m1 = 1400 kg
m2 = 4700 kg
u1 = 17 m/s
u2 = 0 m/s
Using formula for inelastic collision, we have;
m1•u1 + m2•u2 = (m1 + m2)v
Where v is final velocity after collision.
Plugging in the relevant values;
(1400 × 17) + (4700 × 0) = (1400 + 1700)v
23800 = 3100v
v = 23800/3100
v = 7.677 m/s
Kinetic energy before crash = ½ × 1400 × 17² = 202300 J
Kinetic energy after crash = ½(1400 + 1700) × 7.677² = 182,702.62 J
The total amount of energy remains constant in an isolated system. It implies that energy can neither be created nor destroyed, but can be change from one form to another.
Wee can use here kinematics
as we know that

for shorter tree we know that


now since we know that other tree is twice high
So height of other tree is y = 39.2 m
now again by above equation



so the time taken is 2.83 s
Just add all of them up and there is your answer I just added it but I want u to work it out to..