QA: This question is typical on some driver’s license exams: A car moving at 40 km/h skids
12 m with locked brakes.
How far will the car skid with locked brakes
at 80 km/h?
Answer in units of m
QB:A cheerleader lifts his 62.2 kg partner straight
up off the ground a distance of 0.89 m before
releasing her.
The acceleration of gravity is 9.8 m/s
2
.
If he does this 19 times, how much work has
he done?
Answer in units of J
QC:Zak, helping his mother rearrange the furniture in their living room, moves a 49.9 kg sofa
7.1 m with a constant force of 37 N.
What is the work done by Zak on the sofa?
Neglect friction.
Answer in units of J
what is your thinking on these? Surely you do not want us to give you the answers
no i just need help i am completely lost in physics class, and have no clue what he's even talking about. If any one can help explain how to get even one of them that would be great. :)
i still don't have number QA but number QB is 72 and QC is 262.7
QA: To find the distance the car will skid with locked brakes at 80 km/h, we can use the concept of proportionality. The skid distance is directly proportional to the square of the initial velocity.
First, let's calculate the proportionality constant using the given information. The car skids 12 m with locked brakes at 40 km/h.
Proportionality Constant = (Skid Distance) / (Initial Velocity)^2
= 12 m / (40 km/h)^2
= 12 m / (40 km/h) * (40 km/h)
= 12 m / 1600 km^2/h^2
Now, we can use this proportionality constant to find the skid distance at 80 km/h.
Skid Distance at 80 km/h = (Proportionality Constant) * (80 km/h)^2
= (12 m / 1600 km^2/h^2) * (80 km/h) * (80 km/h)
= 12 m / 1600 * 6400 km^2/h^2
= 12 m / 10240000 km^2/h^2
Simplifying further, we convert the units to meters.
Skid Distance at 80 km/h = (12 m / 10240000 km^2/h^2) * (1000 m / 1 km)^2
≈ 0.93 meters
Therefore, the car will skid approximately 0.93 meters with locked brakes at 80 km/h.
QB: To find the work done by the cheerleader, we can use the formula:
Work = Force * Distance * cos(angle)
Here, the force is equal to the weight of the partner, which can be calculated using the formula:
Force = mass * acceleration due to gravity
= 62.2 kg * 9.8 m/s^2
= 609.16 N
The distance over which the work is done is 0.89 m. The angle between the force and the direction of motion is 0 degrees, so the cos(angle) is 1.
Work = 609.16 N * 0.89 m * 1
≈ 542.54 J
Therefore, the cheerleader has done approximately 542.54 Joules of work.
QC: The work done on an object can be calculated using the formula:
Work = Force * Distance * cos(angle)
In this case, the force applied by Zak is 37 N, and the distance over which the force is applied is 7.1 m. The angle between the force and the direction of motion is 0 degrees, so the cos(angle) is 1.
Work = 37 N * 7.1 m * 1
= 261.7 J
Therefore, Zak has done 261.7 Joules of work on the sofa.