A boat is rowed at a velocity of 20 km/hour across a river. The velocity of stream is 8 km/hour. Determine the resultant velocity of the boat.

Question 1 :-  A boat is rowed at a velocity of 20 km/hour across a river. The velocity of stream is 8 km/hour. Determine the resultant velocity of the boat.

Solution:

 Taking downstream direction as x and direction across the river as y, it is given that 

Vx = 8 km/hour Vy = 20 km/hour

 The resultant velocity

 V=√(8²+20²) =21.54 km/hour 

α = tan-¹ Vy/Vx= tan-¹ 20/8 

=68.20°

Question 2:- The guy wire of the electrical pole shown in Fig. 1.9(a) makes 60° to the horizontal and is carrying a force of 60 kN. Find the horizontal and vertical components of the force.

Solution: 

Figure (b) shows the resolution of force 

F = 20 kN 

into its components in horizontal and vertical components. 

From the figure it is clear that 

Fx =F cos 60° =20 cos 60° =10 kN (to the left)

 Fy= F sin 60°  =20 sin 60° = 17.32 kN (downward)