Under which of the following conditions is workdone
A man supports a heavy food above his head with his hands
A boy climbs onto a table
A man pushes unto a table
A woman holds a pot of water
Correct answer is B
For work to be done, distance must be involved because
workdone = force × distance
Under what conditions are cathode rays produced in a discharge tube?
High pressure and low voltage
High pressure and high voltage
Low pressure and low voltage
Low pressure and high volatge
Correct answer is D
Cathode rays are produced in a discharge tube under Low pressure and high voltage
0.8N
2.5N
0.5N
1.0N
Correct answer is C
Upthrust = change in weight
density = massvolume
Mass of liquid displaced = Density of Liquid × Volume;
= 103×50×10−6m3
= 0.05kg
(Note that the volume of 50cm3 was converted to m3 by multiplying by 106) i.e 50cm3=50×10−6m3
Since mass displaced = 0.05kg
Upthrust = mg = 0.05 × 10
= 0.5N
Why do soldiers march disorderly while crossing a bridge?
To prevent resonance on the bridge
To set the bridge into resonance
To make the b ridge collapse
To spread their weight evenly on the bridge
Correct answer is A
Soldiers march disorderly while crossing a bridge to prevent resonance because when soldiers march in orderly manner across a bridge, they generate a rhythmic oscillation of wave on the bridge and at a certain point, would start oscillation to the same rhythm as that of the marching steps. This oscillation would reach a maximum peak when the bridge can no longer sustain its own strength and hence collapses. So for this reasons, soldier are ordered to march disorderly while crossing a bridge.