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May 30, 2015

Posted by **Ariel** on Monday, July 12, 2010 at 2:31pm.

1.)If a blue car drives 10km/h across the deck of an ocean liner that is traveling at 90km/h, what is the blue car's speed relative to the surface of the water when it drives toward the front of the ocean liner?

a)10 km/h

b)80 km/h

c)90 km/h

=d)100 km/h

2.)A motorboat travels at a speed of 40 km/h relative to the surface of the water. If it travels upstream against a current of 12 km/h what is the boats speed relative to the shore?

a)3.3 km/h

=b)28 km/h

c)40 km/h

d)52 km/h

3.)An airplane flies north at a speed of 150 km/h relative to the air through which it flies. If there is a tail wind of 50 km/h, what is the plane's velocity relative to the ground?

a)3 km/h north

=b)100 km/h north

c)150 km/h north

d)200 km/h north

4.)A plane flying 100km/h due north encounters a crosswind of 100km/h "from the east" (i.e. blowing westward). What then, is the plane's velocity relative to the ground?

a)141.4 km/h northeast

=b)141.4 km/h northwest

c)100 km/h northeast

d)100 km/h northwest

5.)A bullet is shot from a rifle aimed horizontally at the same time a bullet is dropped from the same height as the gun's barrel. Which bullet hits the ground first?

a)The fired bullet

=b)The dropped bullet

c)Both bullets the ground at the same time

6.)A car drives off a vertical cliff that is 122.5m tall. If the car lands 100m from the base of the cliff what was the cars speed as it drove off the cliff.

a)20m/s

=b)22m/s

c)24m/s

d)26m/s

(#6 I just really guessed because I don't know what to do so I just 122.5-100=22.5 so I just stuck with that.)

- Physics Check -
**Quidditch**, Monday, July 12, 2010 at 5:30pm#1 correct

#2 correct

#3 wrong

#4 correct

#5 wrong

----

#6

find t in seconds:

122.5m = (0.5)(g)(t^2)

122.5m = (0.5)(9.8m/s^2)t^2

reducing...

25s^2 = t^2

t = +5 seconds and t = -5 seconds

Disregard the negative time.

That is how long it took to fall 122.5m.

So, if the car traveled horizontally 100m in 5 seconds, speed is 100m/5s = 20m/s which is the answer a.

- Physics Check -
**Quidditch**, Monday, July 12, 2010 at 5:42pmA more complete explanation...

The car is traveling horizontally at a constant speed. When it drives off the cliff, it keeps going at the same speed (disregarding friction) until it is stopped by hitting the ground. A forumla for (d) distance traveled with constant acceleration, no initial vertical velocity is:

d = (1/2)(a)(t^2)

where a is the acceleration and t is the time. The acceleration due to gravity is about 9.8m/s^2.

d is given as 122.5m.

Once the falling time is found that can be plugged into the formula for speed.

In this case it took 5 seconds to fall, and the car traveled 100m in that time.

- Physics Check -
**Damon**, Monday, July 12, 2010 at 5:46pmIn number 5 both bullets fall at the same rate. The horizontal problem has nothing to do with the vertical problem except that the time in the air is the same.

- Physics Check -
**Ariel**, Tuesday, July 13, 2010 at 1:01pmThanks:)

- Physics Check -
**ANA**, Wednesday, October 6, 2010 at 1:50pmA motorboat travels at a speed of 40 km/h relative to the surface of the water. If it travels upstream against a current of 12 km/h what is the boats speed relative to the shore?

- Physics Check -
**ANA**, Wednesday, October 6, 2010 at 1:54pmAn airplane flies north at a speed of 150 km/h relative to the air through which it flies. If there is a tail wind of 50 km/h, what is the plane's velocity relative to the ground?

- Physics Check -
**iz**, Tuesday, August 16, 2011 at 12:24pm.)An airplane flies north at a speed of 150 km/h relative to the air through which it flies. If there is a tail wind of 50 km/h, what is the plane's velocity relative to the ground?

200 km/h north

- Physics Check -
**iz**, Tuesday, August 23, 2011 at 12:44pm.)An airplane flies north at a speed of 150 km/h relative to the air through which it flies. If there is a tail wind of 50 km/h, what is the plane's velocity relative to the ground?

150 km/h

- Physics Check -
**your face**, Thursday, January 10, 2013 at 5:56pmwho really cares?