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Mechanics
7 ECAT Physics questions with answers and explanations.
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A ball is thrown vertically upward at 20 m/s. What maximum height does it reach? (g = 10 m/s2, no air resistance)
- 1 10 m
- 2 20 m
- 3 40 m
- 4 5 m
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Correct answer: 20 m
Using v^2 = u^2 - 2gh with v = 0 gives h = u^2 / 2g = 400 / 20 = 20 m.
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A ball is thrown vertically upward at 20 m/s. How long does it take to reach its highest point? (g = 10 m/s2, no air resistance)
- 1 1 s
- 2 4 s
- 3 2 s
- 4 0.5 s
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A 5 kg block slides down a frictionless incline of 30 degrees. What is its acceleration? (g = 10 m/s2)
- 1 5 m/s2
- 2 10 m/s2
- 3 8.7 m/s2
- 4 2.5 m/s2
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Correct answer: 5 m/s2
The acceleration along a frictionless incline is g sin(theta) = 10 x 0.5 = 5 m/s2. The mass does not matter.
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A force of 10 N acts perpendicular to a spanner at a distance of 0.5 m from the nut. What torque is produced?
- 1 20 N m
- 2 5 N m
- 3 0.05 N m
- 4 10 N m
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Correct answer: 5 N m
Torque = force x perpendicular distance = 10 x 0.5 = 5 N m.
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A skater spinning with arms outstretched pulls her arms in. Her angular velocity:
- 1 Decreases
- 2 Stays the same
- 3 Becomes zero
- 4 Increases
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Correct answer: Increases
Angular momentum is conserved. Pulling the arms in reduces the moment of inertia, so the angular velocity must rise.
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A 2 kg ball moving at 3 m/s collides head-on and elastically with a stationary 2 kg ball. What happens?
- 1 Both move at 1.5 m/s
- 2 The first ball stops and the second moves at 3 m/s
- 3 Both stop
- 4 The first ball rebounds at 3 m/s
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Correct answer: The first ball stops and the second moves at 3 m/s
For an elastic collision between equal masses, the velocities are exchanged.
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How much energy is stored in a spring of constant 200 N/m stretched by 0.1 m?
- 1 1 J
- 2 10 J
- 3 20 J
- 4 0.1 J