Question

CLASS WORK

1. A boy of weight, 300N climb's to the top of a hill of weight 20 m. The work done by the boy against the force of gravity is:


2. A body initially at rest is accelerated at the rate of 0.2 metre per seconds square for 5seconds under a constant force of 50N.the work done on the body is

3. An object of mass 20kg is released from a height of 10m above the ground level. The kinetic energy of the object just before it hits the ground is:​

Answer 1

Answer:

1.

work done will be change in potential

W = mgh = 300 × 20 = 6000 J = 6 kJ

2.

First find distance travelled by boy

$s = ut + \frac{1}{2} a {t}^{2} \\ = 0(5) + \frac{1}{2} \times 0.2 \times {5}^{2} \\ = 2.5 \: m$

Now

W = F . S = 50 × 2.5 = 125 J

3.

Assume potential energy is zero at ground .

KE = PE = mgh = 20 × 10 × 10 = 2 kJ

Answer 2

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