Physics
To lift a load of 30 kgf, Suhas uses a single fixed pulley while Radha uses a single movable pulley. The displacement of efforts in both the cases are equal. In an ideal situation calculate the ratio of :
(a) the efforts in the two cases.
(b) the potential energy gained by the loads in the two cases.
(c) the efficiencies in the two cases.
Related Questions
(a) Name the unit of work done, used in subatomic scale.
(b) To which class of lever does a pair of scissors belong?
(c) A stone is tied to a string and displaced from A to B by application of constant force F in three different ways as shown in the diagram below.
Arrange the three cases in ascending order of the work done by the force. (Given AJB is a semi-circle, θ < 90° and AB = 20 m)
A ball of mass 20 g falls from a height of 45 m. It rebounds from the ground to a height of 40 m. Calculate :
(a) initial potential energy of the ball.
(b) the speed of the ball at which it hits the ground.
(c) the loss in kinetic energy on striking the ground.
[g = 10 m s-2]
(a) One end of a plastic foot ruler is held tightly at the edge of a table and the other end is plucked. Name the vibrations produced in the ruler.
(b) Now the ruler is pushed inside partially and plucked again from its freе end. State with a reason whether the frequency of vibration increases or decreases.
Two persons A and B are standing in front of a cliff in the same line 170 m apart as shown in the diagram.
Person B fires the gun and hears the echo in 3 s. Then the person A standing in front of the person B fires the gun.
(Speed of sound in air is 340 m s-1)
(a) Calculate:
- the distance of the person B from the cliff.
- the minimum time in which B hears the gunshot fired by A.
(b) Fill in the blank.
The echo is softer (less loud) than the original sound due to the decrease in …………… [amplitude / frequency] of the wave.