Complete Physics Test - SA II - Class 9 MCQ

When a body moves on a circular path. The force that acts on the revolving body towards the center is called centripetal force. As the force acts as right angle to the direction of motion, so work done is 0.

Crests and troughs are formed in transverse wave. The upward movement from mean position is called crest and downward movement is called troughs.

Work done when a body moves at an angle to the direction of force is W = Fcos? × s. The value of Cos is maximum for 0⁰. So, work done will be maximum for this angel.

Loudness of sound depends upon amplitude. Amplitude is the maximum displacement from mean position.

1 kwH =1000 W × 60 × 60 s= 3600000 J = 3.6 × 10⁶  J. one watt is equal to one joule per second.

Time–period = 0.2/20 = 0.01 second. Frequency = 1/time–period = 1/0.01 = 100Hz.

1 unit (Kw-H) = 3.6×10⁶ joule. Therefore, 250 units = 250 × 3.6 × 10⁶ joule = 9 × 10⁸ Joule.

Wave motion shifts wave energy from one region to another region. Mass is not transferred during wave motion.

Potential energy = mgh, here, P.E = 9800 j. mass = 50kg, g=9.8m/s². Therefore, 9800= 50×9.8×h, h= 9800/50×9.8= 20m.

1 watt second (W.S) = 1 J/s×s joule.

X-rays, light rays are electrostatic waves. These waves do not require material medium for its propagation.

Electron volt is an unit of energy. One electron volt is equal to 1.6 × 10⁻¹⁹ joule.

One mega electron = 1.6×10⁻¹⁹ joule × 100000 = 1.6×10⁻¹³ joules.

Potential energy = mgh, here, P.E = 9800 j. mass = 50kg, g=9.8m/s² .

Therefore, 9800=50×9.8×h, h= 9800/50×9.8 = 20m.

Power = work done / time taken, here, work done = 2000 joule, time = 400 s. power = 2000j/400s = 5 j/s or 5w.

Wavelength= wave speed / frequency,

wavelength=440ms⁻¹ /840Hz = 0.53m.

Distance between two consecutive crests is called wavelength. Here, wavelength= 100 m, wave velocity = 20m/s. frequency = wave velocity/ wavelength. Frequency= 20/100 = 0.2Hz

Initial velocity (u) = 30 km/h = 30×5/18  = 25/3 m/s. final velocity (v) =60 = 50/3 m/s.

mass = 1500 kg. work done = change in kinetic energy 

Distance between two consecutive crests is called wavelength. Here, wavelength= 100 m, wave velocity = 20m/s.

frequency = wave velocity/ wavelength. Frequency= 20/100 = 0.2Hz.

Force is the product of mass and acceleration due to gravity. Mass = 2m and acceleration due to gravity =g m/s².

Force = 2m ×g = 2mg.

The speed of sound is faster in solid medium in comparison to liquid and gaseous medium. Aluminium is solid and metal, so, the speed of sound will be maximum in it.

Mass = 20 kg, height = 20×20/100 m = 4m, time taken = 20 s. power = work done/ time, power = mgh/t. = 20×10×4/20  watt = 40 w.