# Common Science Physics Practice Test 4

Question – 1

1. What would be the work done by a force to stop a car of mass 500 kg moving with a velocity of 24 m/s?

• A. 144000 J

• B. 100000 J

• C. 12000 J

• D. 6000 J

• E. 169000 J

• Answer Explanation:W = KE2 – KE1 Or W = 1/2 m(v2 – u2)
W = 1/2 X 500 X (02 – 242)
Or W = -144000 J
Negative sign is because work is done in stopping the car (retardation). Same would be coming in positive if the work is done in moving the car. Hence, A is the correct answer option.

Question – 2

2. A car starts from a point A at 9 AM and reaches point B at 11 AM. If A and B are separated by 100 km and the car is moving with uniform speed, what is the speed of the car for the entire travel in m/s?

• A. 15.7 m/s

• B. 13.9 m/s

• C. 11.3 m/s

• D. 10.4 m/s

• E. 14.5 m/s

• Answer Explanation:Speed is given as v = d/t
v = 100/2 or v = 50 km/h
Convert hours into seconds and km into m.
50 km/h = 50 X 1000/3600 m/s
or 50 km/h = 13.9 m/s
Hence, B is the correct answer option.

Question – 3

3. A rotor with uniform angular speed of 210 s-1 needs a torque of 250 Nm from an engine. What would be the power of the engine required for the torque?

• A. 54500 W

• B. 52500 W

• C. 34600 W

• D. 1.19 W

• E. None of the above choices

• Answer Explanation:Power associated with torque is given as P = ?? ??
P = 250 X 210
Or P = 52500 W
Hence, B is the correct answer option.

Question – 4

4. What would be the number of electric lines of forces coming out of a unit charge?

• A. 5.5 X 107

• B. 8.5 X 10-7

• C. 2.15 X 107

• D. 1.11 X 10-5

• E. 1.81 X 10-8

• Answer Explanation:Electric lines of forces are nothing but electric flux lines. Electric flux originating from a charge is given as
?? = Q/??0——-(1)
?? = -(1.6 X 10-19) / (8.85 X 10-12) Or ?? = – 1.81 X 10-8
Negative sign signifies that the electric field lines for an electron are inwards rather than outwards. Neglecting the negative sign, number of electric lines of force becomes 1.81 X 10-8. The result suggests that, electric flux for an electron is of a very minute quantity.
Hence, E is the correct answer option.

Question – 5

5. A tuning fork vibrates with a frequency of 500 Hz. If the speed of sound in air is 343 m/s, what is the distance the sound travels when the tuning fork makes 100 oscillations?

• A. 34.3 m

• B. 50.4 m

• C. 5 m

• D. 76.8 m

• E. 68.6 m

v = ????
343 = 500 X ?? Or ?? = 0.686 m
This is the distance which the sound travels in one oscillation. The distance traveled in 100 oscillations is d = 100 X 0.686 m Or d = 68.6 m
Hence, E is the correct answer option.

Question – 6

6. A force acting on a body of mass 10 kg changes its velocity from 3 m/s to 6.7 m/s in 20 seconds. What is the magnitude of the force applied on the body?

• A. 10 N

• B. 3.77 N

• C. 1.85 N

• D. 4.55 N

• E. 2.33 N

F= 10 X (6.7-3)/20
Or F = 1.85 N
Hence, C is the correct answer option.

Question – 7

7. Which of the following is a unit of power?

• A. J

• B. Nm/s

• C. W/s

• D. W/s

• E. None of the above choices

P = W/t and W = F.d
SI unit of force (F) is N, displacement (d) is m and time (t) is s.
Therefore P = Nm/s Or, P = Nm/s
Hence, B is the correct answer option.

Question – 8

Which of the following statement(s) is true in accordance to the given figure?

• A. 2

• B. 1

• C. 3

• D. Both 1 and 2

• E. Both 2 and 3

• Answer Explanation:Force experienced by the beta particle is given as F = qvB sin ??
F = 1.6 X 10-19 X 104 X 0.01 X sin 90o
F = 1.6 X 10-17 X 1 N
F = 1.6 X 10-17 N
Hence, B is the correct answer option.

Question – 9

9. What is the buoyant force exerted on a 20 cm3 block of iron submerged completely inside water?

• A. 0.234 N

• B. 0.111 N

• C. 2.289 N

• D. 1.34 N

• E. 0.196 N

• Answer Explanation:Buoyant force is given as FB = ??gV
As the block is submerged completely, volume of water displaced is equal to the volume of the block = 20 cm3.As the volume is given in cm3 we need to convert it into m3.
FB = 1000 X 9.8 X 2 X 10-5
Or FB = 0.196 N
Hence, E is the correct answer option.

Question – 10

10. A particle in SHM has a time period of 3 s and amplitude of 0.1 m. What is the displacement of the particle after 1 s?

• A. 0.011 m

• B. 0.23 m

• C. 0.087 m

• D. 0.754 m

• E. Zero

y(t) = Asin(2??/T)t
y(1) = 0.1 X sin(2??/3)1
y(1) = 0.1 X ???3/2 Or y(1) = 0.087 m
Hence, C is the correct answer option.

Question – 11

11. Which of the following consist of the highest energy photons?

• A. X-ray

• B. Visible light

• C. Infrared

• E. Microwaves

• Answer Explanation:All of the options given above are electromagnetic waves. They travel at 3 X 108 m/s. Radio waves have energy in order of 10-9 eV (electron-volt) to 10-6 eV. Microwaves have energy in order of 10-5 eV to 10-2 eV. Infrared have energy in order of 1 to 10-2 eV. Visible light have energy in order of 1.6 eV to 3.2 eV. X-rays have energy in order of 102 to 105 eV. Hence on comparing energies of all the electromagnetic waves given above, X-ray has the highest energy. Hence, A is the correct answer option.

Question – 12

12. Consider the figure given below for a system of two iron blocks connected with a common pulley. If the block A weighs 200 N, what would be the mass of the iron block B to keep the whole system in static equilibrium?

• A. 20.41 kg

• B. 15.57 kg

• C. 22.23 kg

• D. 34.45 kg

• E. 21.45 kg

• Answer Explanation:As the whole system is in static equilibrium, there will be no motion in the blocks. In other words, weight of both the iron blocks should be the same.
W = mg
200 = m X 9.8
Or m = 20.41 kg
Therefore, A is the correct answer option.

Question – 13

13. Air is filled in a piston of capacity 100 liters at 313 K. At what temperature should the piston be heated so that volume increases to 120 liters for an isobaric process?

• A. 375.6 K

• B. 373 K

• C. 300.45 K

• D. 413.5 K

• E. 343.7 K

• Answer Explanation:Isobaric process is carried out at a constant pressure. Since, pressure is constant here, we have to apply Charles’s law. According to Charles’ law
V1 / T1 = V2 / T2
100/313 = 120/T2 Or T2 = 375.6 K
Hence, A is the correct answer option.

Question – 14

14. A spring balance measures the weight of a block of ice as 400 N. What is the mass of the block of ice?

• A. 34.65 kg

• B. 45.66 kg

• C. 40.82 kg

• D. 24.87 kg

• E. 76.56 kg

W = mg
400 = m X 9.8
Or m = 40.82 kg
Hence, C is the correct answer option.

Question – 15

15. What would be the power of a convex lens of focal length 10 cm?

• A. -0.2 dioptre

• B. -0.1 dioptre

• C. 10 dioptre

• D. -10 dioptre

• E. 0.05 dioptre

• Answer Explanation:Power of a lens is given as P = 1/??
Power of converging or convex lens is positive. Therefore P = 1/10 cm
SI unit of power is m-1. Hence we need to convert the unit from cm-1 to m-1.
P = 1/0.1 Or P = 10 m-1
There is another SI unit for power which is equivalent to m-1and is known as dioptre.
Therefore P = 10 dioptre. Hence, C is the correct answer option.