A projectile is projected from the ground with speed 20 m/s at an angle 60° above the horizontal. Neglect air resistance and take g = 10 m/s². Its speed when it is at half of its maximum height is:
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Question

A projectile is projected from the ground with speed 20 m/s at an angle 60° above the horizontal. Neglect air resistance and take g = 10 m/s². Its speed when it is at half of its maximum height is:

G1 Physics · Accepted Answer

Maximum height H = u²sin²60°/(2g) = 400×( 3 4 \frac{3}{4} 4 3 ​ )/20 = 15 m. At y = H/2 = 7.5 m, use energy/kinematics: v² = u² - 2gy = 400 - 2×10×7.5 = 250. Therefore v = 5√10 m/s. Hence option A is correct.