Física - Mecânica Practice Questions
ENEM (Brazil) · ENEM Ciências da Natureza · 144 free MCQs with instant results and detailed explanations.
144
Total
53
Easy
68
Medium
23
Hard
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Sample Questions from Física - Mecânica
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Q1
Easy
A car accelerates uniformly from rest and reaches a speed of 20 m/s in 10 seconds. What is the acceleration of the car?
A.
2 m/s²
B.
4 m/s²
C.
10 m/s²
D.
20 m/s²
Show Answer & Explanation
Correct Answer: A
Acceleration is calculated using the formula a = (v - u) / t. Here, v = 20 m/s, u = 0 m/s, and t = 10 s. Thus, a = (20 - 0) / 10 = 2 m/s².
Q2
Easy
A block slides down a frictionless incline of height 5 m. What is the speed of the block at the bottom of the incline just before it hits the ground?
A.
5 m/s
B.
10 m/s
C.
15 m/s
D.
20 m/s
Show Answer & Explanation
Correct Answer: B
Using energy conservation, the potential energy at the top (mgh) converts entirely to kinetic energy at the bottom (1/2 mv²). Setting them equal, we have mgh = 1/2 mv². For h = 5 m and g = 10 m/s², we find v = sqrt(2gh) = sqrt(2 * 10 * 5) = 10 m/s.
Q3
Easy
What is the primary cause of an object's motion in a frictionless environment?
A.
Force applied to the object
B.
The object's weight
C.
Air resistance acting on it
D.
The color of the object
Show Answer & Explanation
Correct Answer: A
In a frictionless environment, the motion of an object is primarily caused by the force applied to it. Without friction, any applied force will result in acceleration according to Newton's second law.
Q4
Medium
A 5 kg object is dropped from a height of 20 meters. Ignoring air resistance, what will be its speed just before it hits the ground? (Use g = 9.8 m/s²)
A.
10 m/s
B.
14 m/s
C.
20 m/s
D.
19.6 m/s
Show Answer & Explanation
Correct Answer: D
Using the formula v = √(2gh), where h = 20 m and g = 9.8 m/s², we find v = √(2 × 9.8 × 20) = √392 = 19.6 m/s. Hence, the speed just before hitting the ground is 19.6 m/s.
Q5
Medium
A car accelerates uniformly from rest at a rate of 3 m/s². How far does it travel in the first 8 seconds?
A.
96 m
B.
48 m
C.
72 m
D.
24 m
Show Answer & Explanation
Correct Answer: A
The distance traveled under uniform acceleration can be calculated using the formula s = ut + 0.5at². Here, u = 0, a = 3 m/s², and t = 8 s. Thus, s = 0 × 8 + 0.5 × 3 × (8)² = 0 + 0.5 × 3 × 64 = 96 m.
Q6
Medium
An object is moving in a circular path with a radius of 10 m at a constant speed of 4 m/s. What is the centripetal acceleration of the object?
A.
1.6 m/s²
B.
0.4 m/s²
C.
16 m/s²
D.
8 m/s²
Show Answer & Explanation
Correct Answer: A
Centripetal acceleration (a_c) is given by the formula a_c = v²/r. Here, v = 4 m/s and r = 10 m. Thus, a_c = (4)² / 10 = 16 / 10 = 1.6 m/s².
Q7
Medium
A 2 kg block slides down a frictionless incline of angle 30 degrees. What is the acceleration of the block down the incline?
A.
4.9 m/s²
B.
9.8 m/s²
C.
0 m/s²
D.
3.9 m/s²
Show Answer & Explanation
Correct Answer: A
The acceleration down the incline can be calculated using a = g * sin(θ). Here, g = 9.8 m/s² and θ = 30 degrees. Therefore, a = 9.8 * sin(30°) = 9.8 * 0.5 = 4.9 m/s².
Q8
Hard
A car accelerates uniformly from rest and reaches a speed of 25 m/s in 10 seconds. What is the total distance covered by the car during this time?
A.
125 meters
B.
250 meters
C.
100 meters
D.
50 meters
Show Answer & Explanation
Correct Answer: A
The distance covered during uniformly accelerated motion can be calculated using the formula: distance = (initial velocity × time) + (1/2 × acceleration × time²). Since the initial velocity is 0, the distance simplifies to (1/2 × acceleration × time²). The acceleration can be calculated as (final velocity - initial velocity) / time = (25 m/s - 0) / 10 s = 2.5 m/s². Plugging this into the distance formula gives distance = (1/2 × 2.5 m/s² × (10 s)² = 125 meters.
Q9
Hard
A 5 kg object is held at a height of 10 meters above the ground. What is its potential energy relative to the ground? (Use g = 10 m/s²)
A.
500 Joules
B.
100 Joules
C.
50 Joules
D.
300 Joules
Show Answer & Explanation
Correct Answer: A
Potential energy (PE) is calculated using the formula: PE = mass × gravity × height. Here, mass = 5 kg, gravity = 10 m/s², and height = 10 m. Therefore, PE = 5 kg × 10 m/s² × 10 m = 500 Joules.
Q10
Hard
A car accelerates uniformly from rest to a speed of 30 m/s over a distance of 150 meters. What is the magnitude of the car's acceleration?
A.
3 m/s²
B.
4 m/s²
C.
6 m/s²
D.
5 m/s²
Show Answer & Explanation
Correct Answer: D
Using the formula v² = u² + 2as, where v = 30 m/s, u = 0 m/s, and s = 150 m, we find that a = (v² - u²) / (2s) = (30² - 0) / (2 * 150) = 5 m/s².
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Física - Mecânica — ENEM (Brazil) ENEM Ciências da Natureza Practice Questions Online
This page contains 144 practice MCQs for the chapter Física - Mecânica in ENEM (Brazil) ENEM Ciências da Natureza. The questions are organized by difficulty — 53 easy, 68 medium, 23 hard — so you can choose the right level for your preparation.
Every question includes a detailed explanation to help you understand the concept, not just memorize answers. Take a timed quiz to simulate exam conditions, or practice at your own pace with no time limit.