A ball is kicked from level ground at 20 m/s at 30 degrees above the horizontal (g = 10 m/s^2, no air resistance). What is its speed when it is 3.2 m above the ground?
Answer and explanation
Correct answer: D. about 18.3 m/s
- Step 1: Mechanical energy is conserved, so the speed depends only on the height gained, not on the launch angle.
- Step 2: v^2 = v0^2 - 2 g h = 400 - 2(10)(3.2) = 400 - 64 = 336.
- Step 3: v = sqrt(336), which is about 18.3 m/s.
Answer
about 18.3 m/s.
Why not the others: '17.32 m/s' is the horizontal component 20 cos 30, the speed at the top; '16.7 m/s' subtracts 64 from the speed instead of from its square; '20 m/s' is the launch speed.
Practise more Classical Mechanics and Electromagnetism.
Free questions with an explanation for every one, and full timed Qatar Senior Secondary Certificate (Thanaweya) mock tests.
More Classical Mechanics and Electromagnetism questions
- A projectile is launched from ground level with an initial velocity of 50 m/s at an angle of 30° above the horizontal. Taking g = 10 m/s^2 a…
- A 1200 kg car rounds an unbanked circular curve of radius 50 meters on a horizontal road. If the coefficient of static friction between the…
- A constant force of 40 N acts on a 5.0 kg body initially at rest for a duration of 3.0 seconds. What is the work done on the body by this fo…
- A simple pendulum has a period of 2.0 seconds at Earth's surface. What would be its period if it were placed on the Moon, where the gravitat…
- Two parallel plates separated by a distance of 5.0 mm have a potential difference of 250 V across them. What is the magnitude of the uniform…
- An electric circuit consists of a 12 V battery connected across two parallel resistors of 6 ohms and 12 ohms. What is the total current draw…