Amass of 4kg suspended by a light string 2m long and at rest is projected horizontally with a velocity of 1.5 m/s. find the angle made by the string when the mass comes to momentary rest

19.5°

Explanation:

The energy of the mass must be conserved. The energy is given by:

1)

where m is the mass, v is the velocity and h is the hight of the mass.

Let the height at the lowest point of the be h=0, the energy of the mass will be:

2)

The energy when the mass comes to a stop will be:

3)

Setting equations 2 and 3 equal and solving for height h will give:

4)

The angle ∅ of the string with the vertical with the mass at the highest point will be given by:

5)

where l is the lenght of the string.

Combining equations 4 and 5 and solving for ∅:

6)

the device is called “ rocket engine”