Answer:
1000 cm.
Explanation:
To obtain the estimated tree height :
(Height of rod / length of rod shadow) = (height of tree / length of tree shadow)
Substituting values into the formula :
(150cm / 120 cm) = (height of tree / 800 cm)
Using cross multiplication :
Height of tree * 120 = 150 * 800
Height of tree = (150 * 800) / 120
Height of tree = 120,000 / 120
Height of tree = 1000
Hence, estimate height of tree = 1000 cm
Answer
a) Using dimensional analysis we cannot derive the relation, But we can check the correctness of the formula.

now, L H S
s = distance
dimension of distance = [M⁰L¹T⁰]
now, equation on the right hand side
R H S
u = speed
u = m/s
Dimension of speed = [M⁰L¹T⁻¹]
dimension of time
t = sec
Dimension of time = [M⁰L⁰T¹]
Dimension of 'ut' = [M⁰L¹T⁻¹][M⁰L⁰T¹]
= [M⁰L¹T⁰]
now, acceleration= a
a = m /s²
dimension of acceleration = [M⁰L¹T⁻²]
dimension of (at²) = [M⁰L¹T⁻²][M⁰L⁰T¹][M⁰L⁰T¹]
= [M⁰L¹T⁰]
hence, the dimension are balanced.
so, L H S = R H S
b) Moment of inertia of hollow sphere = 
Moment of inertia of solid sphere = 
we know,


Torque is the force that causes rotation
If the same amount of torque is applied to both spheres the sphere with bigger moment of inertia would have smaller angular velocity.
Thus the solid sphere would accelerate more.
Answer:
The options are not shown, so i will answer in a general way.
Suppose the case where the forces act in opposite directions, then we need to subtract the forces, and we know that the magnitude of the resultant force will be:
60N - 50N = 10N
Now, suppose the case where both forces act in the exact same direction, in that case, we will add the forces to get:
60N + 50N = 110N
Then the only range of forces that we can get in this system, are the forces such:
10N ≤ F ≤ 110N
Any resultant force outside that range is not possible in this situation.