physics
posted by Anonymous .
ques 1.......a boy walks from his home to his school at an average speed of 10 km per hour and returns to his home at an average speed of 15 km per hour . what is his average speed in km per hour during the entire round trip ?
ques 2........a thief running at a speed of 8 km per hour is chased by a police man whose speed is 10 km per hour if the thief is 100 metre ahead of the policemen what is the time required by the police men to catch the thief ?
ques 3....a man of mass 60 kg jumps at a speed of 4 meters per second from a stationary boat and as a result the boat moves off with a speed of 0.8 meters per second. what is the mass of the boat?
ques 4.....two persons start walking at a speed of 3 km per hour from a road intersection along two road that make an angle of 60 degree with each other . what will be the shortest distance separating them at the end of 20 minutes?
ques 5....a car starts at rest and moves on a straight road with a uniform acceleration of 10 m/s square for the first 10 seconds . during the next 10 seconds , the car moves with the velocity it has attained . what is the total distance covered by car in 20 seconds ?
ques 6....a crane can raise a load of mass 120kg vertically upward with a speed of 5 metres per second . if the acceleration due to gravity is 10 m/s square what is the power ( in kilowatts ) of the engine ?
ques 7.....water in a river is flowing from west to east at a speed of 5 metres per minute. a man on the south bank of the river , capable of swimming at a speed of 10 mete per minute , wishes to cross the river in the shortest possible time . in which direction must be swim ?
ques 8....a string can withstand a maximum tension of 25N . what is the greatest speed at which a body of mass 1kg can be whriled in a horizontal circle using 1 metre length of the string?
ques 9.....the escape velocity for a body projected vertically upwards from the surface of the earth is ve . if the body is projected in a direction making at angle of 30 degree with the vertical, what is the escape velocity ?
ques 10....the work done in a raising a body of mass 2kg to a height of 1 metre above the ground is ? (
the accelration due to gravity is to m/s square.
ques 11 ...a sound generator placed under water has a frequency of 580 hz. it produces waves of wavelength 2.5 m. what is the speed of sound in water ?
ques 12 ...a man standing in front of a high wall fires a gun. he hears the echo 2 seconds after the gun is fired . if the speed of sound is 340m/s . how far is the wall from the man. ?
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answers
1 12
2 3min
3 300kg
41km
51500m
66kilowatt
75m/s
811.2km/s
920 joule
101450m/s
11340m

1. Avg = (10+15) / 2 = 12.5km/h.
2. 100m = 0.1km.
d1 = V*t + 0.1 = 8t + 0.1 = The thief's distance at end of chase.
d2 = 10t = Policeman's distance at end of chase.
10t = 8t + 0.1,
10t  8t = 0.1,
2t = 0.1,
t = 0.05h = 3min.
3. The velocity is inversly proportional to the mass:
Mass = (4/0.8) * 60kg = 300kg.
4. d = 3km/h + (20/60)h = 1km.
5. d1 = Vo*t + 0.5at^2,
d1 = 0 + 0.5*10*(10)^2 = 500m.
V1 = at = 10 * 10 = 100m/s.
d2 = Vo*t = 100m/s * 10s = 1000m/2.
Dt = d1 + d2 = 500 + 1000 = 1500m.
6. F = mg = 120kg * 10N/kg = 1200N.
Po = = FV = 1200 * 5m/s = 6000 Watts =
6 Kilowatts.
10. F = mg = 2kg * 10N/kg = 20N.
W = Fd = 20 * 1 = 20 Joules.
11. L = VT = V*(1/f) = 2.5m,
V*(1/580) = 2.5,
V = 2.5 * 580 = 1450m/s.
12. T = 2s / 2 = 1s = Time to reach the wall.
d = VT = 340m/s * 1s = 340m.
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