A river is 0.76 km wide. The banks are straight and parallel. The current is 4.0 km/h and is parallel to the banks. A boat has a maximum speed of 3.0 km/h in still water. The pilot of the boat wishes to go on a straight line from A to B, where AB is perpendicular to the banks. What should the pilot do?(adsbygoogle = window.adsbygoogle || []).push({});

a-Take none of these actions.

b-Head 22° upstream from the line AB.

c-Give up-the trip from A to B since it is not possible with this boat.

d-Head directly across the river.

e-Head 68° upstream from the line AB.

What I did:

Since I know it forms a right triangle where

angle theta is unknown

4km/h is the adjacent and .76km is the opposite

so I did inverse tan 4/.76 and got 79 degrees.

-------------------------------------------------

Which of the following statements are true? (Select all that apply and ignore any effects due to air resistance.)

a-When a projectile is fired horizontally from a certain height, it has a higher speed upon reaching the ground than does an identical projectile dropped from rest from the same height.

b-None of these statements are true.

c-When a projectile is fired from a certain height at an upward angle, it takes longer to reach the ground than does an identical projectile dropped from rest from the same height.

d-When a projectile is fired horizontally, it takes the same amount of time to reach the ground as an identical projectile dropped from rest from the same height.

I chose C & D but it was wrong.

I chose C because if shot in an upward, it takes extra time to reach its highest point where velocity is 0, then from there is the same as dropping from rest.

I chose D because the only acceleration is from gravity so it would take the same amount of time to reach the ground.

Am I wrong?

**Physics Forums | Science Articles, Homework Help, Discussion**

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

# Homework Help: Projectile motion river help

**Physics Forums | Science Articles, Homework Help, Discussion**