Tag: common machines

A crow-bar of length $2.0$ m is used as a machine to lift a box of $100$ kgf by placing a fulcrum at a distance of $0.1$ m from the box. Calculate the effort required.

A nut can be opened by a lever of length $0.25$ m by applying a force of $80$ N. What should be the length of the lever if a force of $32$ N is enough to open the nut?

A rubber ball dropped from a height of $20\ m (g = 10\ m/s^{2})$ falls on the roof of an elevator going up at $2\ m/s$. If the collision of the ball with the elevator is elastic, the ball rebounds with a velocity of

Efficiency of engine is $\eta _1$ at $T _1 = 200^\circ C$ and $T _2 = 0^\circ C$ and $\eta _2$ at $T _1 = 0^\circ C$ and $T _2 = -200 K$. Find the ratio of $\dfrac{\eta _1}{\eta _2}$.

A man of mass $80kg$ carrying a load of $20kg$ walks up a stair case in $20s$. If the number of steps is $40$ and width and height of each step are $20cm$ and $15cm$ respectively. The efficiency of the man is

A man uses a crowbar of length $1.5m$ to raise a load of $75kgf$ by putting a sharp edge below the bar at a distance $1m$ from his hand. Calculate the mechanical advantage. 

A water -pump driven by petrol raises water at a rate $ 0.5 m^3/min $ from a depth of 30 m. if the pump is 70% efficient, what power is developed by the engine?

A $20\ N$ metal block is suspended by a spring balance. A beaker containing some water is placed on a weighing machine which reads $40\ N$. The spring balance is now lowered so that the block gets immersed in the water. The spring balance now reads $16\ N$. The reading of the weighing machine will be 

A man uses a crowbar of length $1.5m$ to raise a load of $75kgf$ by putting a sharp edge below the bar at a distance $1m$ from his hand. Calculate the effort needed.

A boy can exert a maximum effort of $250\  N$, so he uses an inclined plane to lift the load up. What should be the minimum length of the plank used by him to lift a mass of $ 50 \ kg$ to a height of $1 \ m$ ?