Answer:
![\theta=28.07^(\circ)](https://img.qammunity.org/2020/formulas/physics/college/w3bch0jnv84z3km82mqnrje7e3n4ew3a59.png)
Step-by-step explanation:
Speed of van, v = 28 m/s
Radius of unbanked curve, r = 150 m
Let
is the angle with the vertical. In case of banking of road,
.............(1)
And
..........(2)
From equation (1) and (2) :
![tan\theta=(v^2)/(rg)](https://img.qammunity.org/2020/formulas/physics/college/92sr6rnxze5mczlqbal91eb0y9tnxhwrfy.png)
![tan\theta=((28)^2)/(150* 9.8)](https://img.qammunity.org/2020/formulas/physics/college/teh7k9dn0ov9ccsk2z3h0ngrvyzpe1be1n.png)
![\theta=28.07^(\circ)](https://img.qammunity.org/2020/formulas/physics/college/w3bch0jnv84z3km82mqnrje7e3n4ew3a59.png)
So, the string makes an angle of 28.07 degrees with the vertical. Hence, this is the required solution.