Question

Sam uses lift to move from 2nd floor to 4th floor. What will be the change in his potential energy?
Take mass of Sam = 50 kg, Height of each floor 7 m and g = 10 ms${}^{-2}$.

• A. - 7000 J
• B. 1400 J
• C. 7000 J
• D. - 1400 J

Answer 1

The correct option is C 7000 J

Given : Mass of Sam = 50 kg,
Height of each floor 7 m,
g = 10 ms${}^{-2}$

Sam is going from 2nd floor to 4th floor.
Hence, the total height travelled by Sam = height of 4th floor (h${}_2$) - height of 2nd floor (h${}_1$)
=> (h${}_2$ - h${}_1$) = 4 x 7 - 2 x 7 = 14 m

Thus, the change in his potental energy = Final potential energy - Initial Potential Energy
= mg(h${}_2$ - h${}_1$) = 50 x 10 x 14 = 7000 J