physics volume 3b work, p, energy key

7/25/2019 Physics Volume 3B Work, P, Energy Key

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K-12 Education Management Pvt. Ltd. 1

DTP-7 (1) -- IX-Clsss Solutions, W, P, Energy

Physics--Volume--3B

PHYSICS VOLUME--3B

VOLUME-3B - SOLUTIONS

WORK, POWER, ENERGY

Clarity Achiever - I

1) c 2) c, d 3) a, c, d 4) a 5) a 6) d 7) c 8) c 9) b 10) c

Application Skill Achiever - I

1) (b) 196 J 2) (c) zero

3) (b) 400 J 4) (d)

5) (c) 40 J 6) (c) zero

7) (c) w F.S

= 5i 5j . i j

= 0 J

8) (a)

w = mg sin s

= 0.250.05

310

5

= 1.5 J

s

mg sin

9) (c)

10) (d)

a =1

V

t

F = ma =1

mv

t

2 2

1

1 1 vS at t

2 2 t

W = F. S. =

(i)2

1 1

mv 1 vt

t 2 t (ii)

2

1

1 vtm

2 t

IX CLASS FINALISED KEY WITH SOLUTIONS-VOLUME-3B


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2 K-12 Education Management Pvt. Ltd.


Physics--Volume--3B

VOLUME--3B PHYSICS

Clarity Achiever - II

1) a, b, c 2) d 3) c 4) a 5) a

Application Skill Achiever - II

1) c 2) c 3) b, d 4) b 5) a

6) c

7) Both A & R are false

8) b 9) c 10) a

Clarity Achiever - III

1) a 2) b 3) b 4) a 5) a

Application Skill Achiever - III

Silver Package :

1) (d)W = mgh = 10 9.8 20

= 98 20

= 1960 J

2) (b)

k = 100 N/m

x = 10 cm

= 10 102m

W =1

2 kx2

=1

2100 (10 102)2

=1

2100 102

=1

2J

3) (a)

W = (P.E.) =

mgh

h1

R

= mgR

h R2

W = Gain in P.E.

= GMm1 2

a 1

r r


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Physics--Volume--3B

PHYSICS VOLUME--3B

=1 1

GMmR 2R

= 2GMm GM mR mgR2R R 2 2

4) (b)

u = GMm

r

1u

r

1 2

2 1

u r 42 : 1

u r 2

5) (a)

W =1

2mgl

=1

5 10 3 75J2

Gold Package :

6) (d)

Elastic Potential energy =1

F2

l

= 31

200 1 102

= 0.1 J

7) (b)

s = ut +1

2at2

h = ut 1

2gt2

= (20) 2 1

2(10) 4

2

= 40 20 = 20 m

P.E. = mgh = 2 (10) (2) = 400 J


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Physics--Volume--3B

VOLUME--3B PHYSICS

8) (b)

W =2 2

2 1

1k x x

2

= 2

2 21 800 15 10 5 102

=4 4400 225 10 25 10

=4400 200 10

= 4 48 10 10

= 8 J

W 8J

Platinum Package :

9) (a)

Work done in climbing up a hill (w)

= (mm+ m

b) gh

= (55 + 25) 10 20

= 80 20 10

= 16000 J

= 16 kJ10) (d)

W = (mm+ m

l) gh

= (60 + 20) (10) 20 20 102

= 80 40 102102

= 3.2 kJ

Clarity Achiever - IV

1) a 2) b 3) d 4) b 5) c 6) a 7) c 8) a, b, c 9) d 10) b

Application Skill Achiever - IV

Silver Package :

1) (a)

21 mv K.E.2

21

50 v 6252

v2 = 25

v = 5 m/s


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Physics--Volume--3B

PHYSICS VOLUME--3B

2) (a)

v = 54 km/h

=

5

54 15m / s18

m = 40 kg

K.E. =21 mv

2

= 21

40 152

= 20 225

= 4500 J

3) (d)

K.E. 2

K1. K

2= 1 : 4

4) (c)

21 m2

1

2 10 4

2

20 J

5) (d)

8

10

K.E. =1

263

8

10

= 19.25

6) (b)

7) (b)

a =

26

2

300 90 10

2 2 10 4

a =

2

2 s


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Physics--Volume--3B

VOLUME--3B PHYSICS

69 10

4

2

2 2 18

29

10

2 49 9 10

29 10 900 m / s

8) t = 3

u = 0

a = 9.8 m/s2

= 4 = 3 98

K.E. =1

2mb2

=1

2 3(3 9.8)2

= 1296.5 J

9) (b)

m2m

1, K.E. = k

1speed =

1

2

Mm K.E. k

2 speed =

2

21

kk

2

=1

m2

2

1

1 1 mv

2 2 22v

2

=2

1

vv

2

=1

m

2

2

1

1 mv 2

2

2

2v

2

=2

1 1

2

vv 2 2 v

v

= 12 1 v 2

v = 2 2 1 m / s


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Physics--Volume--3B

PHYSICS VOLUME--3B

10) (d)

a =1

2

v = at = 5

K.E. =1

2mv2 =

1

2 10 52 = 125 J

CONVEPT V

Clarity Achiever

1) A 2) A 3) A 4) A 5) A

Application Skill Achiever

1) (d)

Force = 200 N, Velocity = 20 ms1

Power = F.V.

= 200 20

= 4000 Watts.

2) (c)

Instantaneous Power = Ins. Force Ins. velocity

= 5i 3j 6k 10i 10 j 20k

= 5 10 i 3 10 j 6 20 k

= 50i 30 j 120k

= 50 30 120 i j k = 140 W

3) (d)

M1= 80 kg, t

1= 15 s

M2= 80 kg, t

2= 20s

Power of M1= 80 15 = 1200

Power of M2= 80 20 = 1600

Rate of their powers =1

2

M 1200 3

M 1600 4

4) (d)

P = F v

P 7500F 375 N

V 20


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Physics--Volume--3B

VOLUME--3B PHYSICS

5) (b)

1 KWH =5

12 746 80 60 60 10

36 10

=746 3 12 35808

100 50

= 716.16 KWH 0.50 Ps.

= Rs. 358.08 Ps.

Gold Package :

6) (d)

P = F v

= mv2

= 225 10 240 500

=

2211 n mvmv

W 22Pt t t

=

221240 5 10 500

2

60

= 120

2

2

5 250000 1060

= 10 2500 = 25000 W.

7) (d)

WP

t

n 2.42

60

2 60 60vn 502.4 12

n 50

8) (b)

2 21 1K.E. mv mv2 2

6 2 6 21 1

2.05 10 25 2.05 10 52 2

5 60


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Physics--Volume--3B

PHYSICS VOLUME--3B

= 6

12.05 10 625 25

2

5 60

= 61 2.05 10 600

2 600

= 62.05 10

= 2.05 Mw

Platinum Package :

9) (d)

d = 200 m t = 1 Min 57.56 Sec = 60 + 57.56

= 117.56 sec

200

117.56 = 1.701 m/sec

WP

t

P = F v

F =P 460v 1.7

= 270 N

10. (d)

Given h = 50 m, M = 1.8 105kg

PE = mgh

Electric energy =PE

2

Electric energy/Sec =PE 1

2 3600

No. of bulbs =PE 1 1

2 3600 100

=

51.8 10 9.8 50 1 1

2 3600 100

=18 10 1 1

9.8 5010 2 3600 100


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Physics--Volume--3B

VOLUME--3B PHYSICS

=549 1 1 10

100 2 200

=

5

5.449 10 49 4901040,000 4 4

No. of bulbs =490

122.54

means 123

CONVEPT VI

Clarity Achiever

1) b 2) a 3) c 4) b 5) d

Silver Package :

1) (b)

Mass of scooter = 80 kg

Mass of scooter + Petrol =64

150 kg

K.E. =2 21 1mv mv

2 2

= 2 21

150 10 5

2

= 75 (100 25)

= 75 75 = 5625 J

2) (b)

M = 0.5 kg, S = 2m

u = 2 m/sec2

KE =1

2mv2

= 12

(0.5) (2)2

= 1 J

3) (c)

F = 10 N, u = 5 m/s, m = 4 kg

v = 5 m/s

KE =1

2mv2

1

2mv2


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Physics--Volume--3B

PHYSICS VOLUME--3B

F.S. =1

2m (v2 u2)

= 2 2 2 21 1m v u 4 10 52 2S

F 10

=100 25 75

15m5 5

4) (c)

W =2 21 1mv m

2 2

F.S. = 12

m (v2 u2)

Case (i) =1

2m (202 102)

=1

2m (400 100)

W1=

1

2m 300

Case (ii) =1

2m (102 02)

W2=

1

2m (100)

Compare Case (i) / Case (ii)

1

2

1 / 2 m 300w 300

w 1/ 2m 100 100

21

300 ww

100

1 2w 3w

3 times of w2

5. (a)

mg h = ma

mgh h = mgh


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Physics--Volume--3B

VOLUME--3B PHYSICS

air

h5 10 20 5 2.5 20

w

100 wair = 250w

air= 1000 250 = 750 J

Gold Package :

6) (a)

mgh = wair

= mgh

wR

= gh ah

= h (g a)

= 200 25104

= 20040 25

50 154

= 750 J

7. (c)

Mass of ship = 3 107 kg

u = 0

s = 3 m

f = 5 104N

W =2 21 1mv mv

2 2

f s =21 mv 0

2

mv2 2f s

v2 = 2f sm

V =

4

7

2f s 2 5 10 3

m 3 10

= 5 7 2 110 10 10

= 0.1 m/s


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Physics--Volume--3B

PHYSICS VOLUME--3B

8) (a)

W =2 21 1mv mv

2 2

F.S. =1

2m (v2 u2)

Case (i) =1

2m (202 102)

=1

2m (400 100)

W1

=300m

2

Case (ii) =1

2m (152 52)

=1

2m (225 25)

W2=

200m

2

1

2

w 300 mw

2

2200 m

300200

1

2

w 3

w 2 w

1: w

2= 3 : 2

w1=

11

2w

2

1

12

times

Platinum package

9) (b)

V 2gh

= 2 10 3.2

= 6.4 10 64

= 8 m/sec.


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Physics--Volume--3B

VOLUME--3B PHYSICS

mgh =21 mv

2

2

v 2gh

= 2 10 3.2

= 6.4 10 64 = 8 m/sec.

10) (b)

Mass of a bullet m = 10 g

=10

0.01 kg1000

wair

resistance =21 mv

2

21 mv2

= 1

0.01 10, 00, 000 2, 50, 0002

=1

0.01 7,50,0002

= 3,75,000 0.01

= 3750 J

CONVEPT VII

Clarity Achiever

1) c 2) b 3) a, c 4) b, c, d 5) d

6) c 7) d 8) d 9) a 10) a

Silver Package :

1) (d)

m = 50 kg,

l = 15 m 13

= 5 m

K.E. = ?

K.E. =PE

2P.E. = mgh

= 50 10 5

= 5000 J

K.E. =PE

2

=5000

2500 J

2


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Physics--Volume--3B

PHYSICS VOLUME--3B

2) (c)

21

kx mg h x2

1

2(0.1)2= 1 x 100 (50 102)

k =10

1000 N /m0.01

3) (a)

4) (a)

5) (a)

Gold Package :6) (b)

mgh =21 mv

2gh =

21 v2

v 2gh 2 10 0.5

5 2 10 m / sec

7) (b)

KE = PE changes

21 mv2

= mgh2 mgh

1

21 v2

= gh2 gh

1

v2 = 2g (h2 h

1)

v = 2 12g h h

= 2 10 2 0.75

= 20 1.25 = 25 = 5 m/sec

8) (a)

2 1v 2g h h

= 2 10 0.1 2

= 1.414 m/sec.

physics volume 3b work, p, energy key

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