Answer:
A) 72° or 71.56°
Explanation:
We have two components on the X-axis and y-axis respectively. So we can use the tangent of the angle to be able to find the angle with respect to the horizontal component.
Ax = 2.5
Ay = 7.5
tan(α) = 7.5/2.5

α = 71.56°
Answer:
a) Maximum height reached above ground = 2.8 m
b) When he reaches maximum height he is 2 m far from end of the ramp.
Explanation:
a) We have equation of motion v²=u²+2as
Considering vertical motion of skateboarder.
When he reaches maximum height,
u = 6.6sin58 = 5.6 m/s
a = -9.81 m/s²
v = 0 m/s
Substituting
0²=5.6² + 2 x -9.81 x s
s = 1.60 m
Height above ground = 1.2 + 1.6 = 2.8 m
b) We have equation of motion v= u+at
Considering vertical motion of skateboarder.
When he reaches maximum height,
u = 6.6sin58 = 5.6 m/s
a = -9.81 m/s²
v = 0 m/s
Substituting
0= 5.6 - 9.81 x t
t = 0.57s
Now considering horizontal motion of skateboarder.
We have equation of motion s =ut + 0.5 at²
u = 6.6cos58 = 3.50 m/s
a = 0 m/s²
t = 0.57
Substituting
s =3.5 x 0.57 + 0.5 x 0 x 0.57²
s = 2 m
When he reaches maximum height he is 2 m far from end of the ramp.
Answer:
Frictional force will be equal to 126.04 N
Explanation:
We have given mass of the bullet m = 28 gram = 0.028 kg
Initial velocity u = 55 m /sec
Width of sand = 30 cm = 0.3 m
So initial kinetic energy 
Final velocity of the bullet v = 18 m /sec
So final kinetic energy 
So change in kinetic energy = 42.35 - 4.536 = 37.814 j
From work energy theorem this change in kinetic energy will be equal to work one by frictional force
So 
