Physics 20 - Lesson 17Vertical Forces and Inclines – Answer Key

Possible 81 / 711) 2 marks each for a total of 14 marks

Dr. Ron Licht Answer Key 17 - 1 www.structuredindependentlearning.com

A. Static

E. Static

B. Static

C. Sliding without friction. D. Static friction prevents sliding.

F. Tied to a rope and pulled straight upward. Accelerating upward at 9.81 m/s2 . No friction.

G. Tied to a rope and pulled straight downward. Accelerating downward at 19.62 m/s2. No friction.

Fg

FN

Fg

FgFg

FN

Fg

FT

Fg

Fg

FT

FNFN

FNFblock on rock

Ff

2)

/5

3)

/6

4)

/6

5)

/11

6)

Dr. Ron Licht Answer Key 17 - 2 www.structuredindependentlearning.com

FT

Thrust ( )

75N 360N

150N

150N

FT

Constant velocity

a)

Since constant velocity is dynamically the same as zero velocity, (b) and (c) are the same as (a).

b)

c)

d)

e)

FT

(-)

(+)

NF

fFcos 24.5cos60

12.26

12.26

y g

y

N

F F

F N

F N

22.5 (9.81 )

24.5

mg s

g

F kg

F N sin 60

21.24

x g

x

F F

F N

Friction Force

0.12(12.2 )

1.47

f n

f

f

F F

F N

F N

Acceleraton

2

21.24 ( 1.47 ) 2.5

7.91

net

ms

F maN N a

a

/4

7)

Bonus /10

8)

/8

Dr. Ron Licht Answer Key 17 - 3 www.structuredindependentlearning.com

a) b)

c) If the cable snaps

(+)

(–)

NF

fFcos 49.05cos50

31.53

31.53

y g

y

N

F F

F N

F N

25.0 (9.81 )

49.05

mg s

g

F kg

F N sin 60 49.05 sin 60

37.57

x g

x

F F N

F N

Friction Force

0.10(31.53 )

3.15

f n

f

f

F F

F N

F N

Acceleraton

2

37.57 ( 3.15 ) 5.0

6.88

net

ms

F maN N a

a

9)

/8

10a)

/6

10b) Refer to #10aThe frictional force acts in the opposite direction

/3

Dr. Ron Licht Answer Key 17 - 4 www.structuredindependentlearning.com

(-)

(+)