A body is projected with a speed u m/s at an angle β with the hor...
A body is projected with a speed u m/s at an angle β with the hor...
Given data:
- Initial speed of projection (u)
- Angle with the horizontal (β)
- Kinetic energy at the highest point is 3/4th of the initial kinetic energy
Understanding the problem:
- At the highest point, the body has maximum potential energy and zero kinetic energy.
- So, kinetic energy at the highest point is equal to the initial kinetic energy minus the potential energy at the highest point.
Solution:
- Let the initial kinetic energy be K.
- At the highest point, kinetic energy = 3/4 * K
- Potential energy = K - 3/4 * K = 1/4 * K
- At the highest point, kinetic energy = potential energy
- Using trigonometry, we can relate the kinetic energy at the highest point to the initial kinetic energy.
Calculation:
- Let's assume the initial kinetic energy be K.
- Using the formula for kinetic energy (K = 1/2 * m * u^2), we can write the kinetic energy at the highest point as 1/2 * m * (u * sin(β))^2.
- Given that this kinetic energy is 3/4 of the initial kinetic energy, we have: 1/2 * m * (u * sin(β))^2 = 3/4 * K
- Simplifying the equation, we get: sin(β)^2 = 3/2
- Solving for β, we find that β = 30°.
Therefore, the value of β is 30° (Option A).