Solution:

Here,

Load lifted (F) = 500 N

Height (h) = 40 m

Time (t) = 2 minutes = 2 x 60 s = 120 s

Work done (W) = F x h = 500 x 40 = 20 000 J

To find: Power (P) = ?

We know,

Power (P) = W / t = (20000 / 120)

= 166.67 W

Hence, the required power of the machine is 166.67 Watt.

When a person carries load and stands for any interval of time, total work done is zero. By definition, work is defined as the scalar product of Force and displacement. However, in this case, there is no displacement because the person is stationary which results in 0 work done.

Solution:

Given,

mass of car (m) = 1500 kg

velocity of car (v) = 72 km/hr = 72 * 1000/3600 (m/s) = 20 m/s

To find: Kinetic Energy of car (KE) = ?

We know,

KE = 1/2 m(v)²

= 1/2 (1500) (20)²

= 300 000 J

= 3 x 10⁶ J

Hence, the required Kinetic Energy of the car is 3 x 10⁶J.

Various types of works are:

1. Work done against friction
2. Work done against gravity

Work done against friction:When a body is moved in the direction of application of force against friction, then the work done is said to be work done against friction. It is not necessary to raise the height of a body in this condition, the body needs to slide over another surface. Example: pushing or pulling a book on the table, etc.

Work done against gravity: When a body is raised to a certain height against the...

The potential energy of an object kept on the Earth's surface is 0 because it has not been displaced to any height.

We know, Potential Energy (PE) = mgh

At the surface of the Earth, h = 0

So, PE = mg * 0

= 0

The kinetic energy increases by 9 times when the velocity of a moving body is trippled.

Mathematical expression for Kinetic Energy (KE) = 1/2 m(v)²

When the velocity of body is trippled, new velocity (v') = (3v)

So, new Kinetic Energy (KE') = 1/2 m(v')²

= 1/2 m(3v)²

= 1/2 m(9v²)

= 9 . 1/2 m(v)²

= 9 KE

While stretching the catapult, potential energy is stored in it. This energy is obtained by doing work against the restoring force of the string.