sample question from class 9 chapter 7 work

Kriti

Asked: September 14, 2026In: Class 9 Science

A coconut of mass 1.5 kg falls from the top of a coconut tree onto the wet sand on a beach. The height of the tree is 10 m. On impact, the coconut comes to rest by making a depression in the sand. (i) Calculate the velocity of the coconut just before it hits the sand. (ii) Assume that the average resistive force of sand is 3000 N and all of the coconut’s energy is used to create the depression in the sand. Calculate the depth of the depression the coconut makes in the sand. Assume g = 10 m s-2.

The impact velocity is 14.14 m s-1, derived from square root of two g h. Total kinetic energy equals 150 J, which divided by 3000 N resistive force gives a sand depression depth of 0.05 m.

Ayushree

Asked: September 12, 2026In: Class 9 Science

A student is slowly lifted straight up in an elevator from the ground level to the top floor of a building. Later, the same student climbs the staircase, all the way to the top. Given that the height of the building is h = 72.5 m, acceleration due to gravity is g = 10 m s-2 and student’s mass is m = 50 kg. (i) Find the gain in the potential energy if the student is lifted straight up to the top. (ii) Find the gain in the potential energy when the student climbs the stairs to the same top. (iii) What do you conclude about the dependence of the potential energy on the path taken?

The gain in potential energy is 36250 joules in both cases, calculated by multiplying mass, gravity and height. Gravitational potential energy depends only on vertical height and is completely independent of the path taken.

Ayushree

Asked: September 12, 2026In: Class 9 Science

Fill in the blanks. (i) Work done = ___ multiplied by _ (in the direction of force).(ii) 1 joule of work is done when a force of _ newton displaces an object by 1 metre in the direction of the force. (iii) The expression for kinetic energy of a body of mass m and velocity v is _. (iv) The potential energy of an object of mass m at a small height h from the Earth surface is _. (v) Power is defined as the ___ at which work is done.

The correct filled terms are force and displacement for part one, one for part two, half m v square for part three, m g h for part four and rate for part five respectively.

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