Physics - Study Mode
[#1146] A device used for converting a.c. into d.c. is called
Correct Answer
(B) Rectifier
Explanation
Solution: A rectifier is an electrical device that converts alternating current (AC), which periodically reverses direction, to direct current (DC), which flows in only one direction. The process is known as rectification, since it "straightens" the direction of current.
[#1147] While catching a ball, a player pulls down his hands to lower the–
Correct Answer
(B) Momentum
Explanation
Solution: A cricketer lowers his hands while taking a catch to decrease the rate of momentum. Cricketers increase the time by pulling their hand's backward with the ball while taking a catch. Linear momentum or translational momentum is the product of the mass and velocity of an object.
[#1148] Momentum is measured as the product of :
Correct Answer
(C) Mass and velocity
Explanation
Solution: The unit of momentum is the product of the units of mass and velocity.
[#1149] Two stones of different masses are dropped simultaneously from the top of a building
Correct Answer
(C) Both the stones reach the ground at the same time
Explanation
Solution: Both stones reach the ground at the same time. The initial speed is 0 for both stones, and the only acceleration working in that system would be g (Gravity acceleration). So, as the distance is the same, the final speed will be the same time. The only reason which could change this result is a difference in the shape of the stones. While they fall to the ground, they must “open” a way across the air. The shape of the falling object will decide the force needed to open that way. This is called the “Air resistance”. Depending on the shape of the object, the resistance force will be bigger or smaller. As this force works counter to g, the falling time will decrease. Between a feather and a plumb ball, the falling time will be the same in vacuum, but inside air, the resistance force for the feather has almost the same value than gravity, while for the ball, the resistance is very much weaker than gravity.
[#1150] A man jumping out of a moving train is thrown
Correct Answer
(A) Forward
Explanation
Solution: When a man jumps out of a moving train, his feet suddenly comes to rest on touching the ground. But, the upper part of the body continues to be in motion and has a tendency to move forward. That is why the person falls with his head forward.