What is the power input at time t=3s for the force of 5N on an 8kg object?

AI Thread Summary
The discussion focuses on calculating the power input for an 8kg object subjected to a 5N force over time. Participants are attempting to derive the object's velocity as a function of time and express power as a function of time, particularly at t=3s. They also discuss a car's performance, needing to calculate the power developed by its engine and its speed after 4 seconds, assuming constant power. Key equations include relating power to work and kinetic energy, with emphasis on using acceleration to find velocity. The conversation highlights the importance of understanding how kinetic energy changes over time in relation to the force applied.
nns91
Messages
301
Reaction score
1

Homework Statement



1. A single force of 5N acts in the x direction on a 8kg object. (a) If the object starts from rest at x=0 at time t=-, find its velocity v as a function of time. (b) Write an expression for the power input as a function of time. (c) What is the power input of the force at time t=3s

2.A car manufacturer claims that his car can accelertate from frest to 100 km/h in 8s. The car's mass is 800kg.

(a) Assuming that this performance is achieved at constant power, determine the power developed by the car's engine.
(b) What is the car's speed after 4s (neglect friction and air resistance)

Homework Equations



p=W/t


3. The Attempt at a Solution [/b

1. I could not even do part a of number 1. Can you guys help me ?

2. So since it's constant power P=W/t. W can be calculated by 1/2 mv^2 right ?

How can I do part b ? Do I just use the P from previous calculation and multiply by time 4 s to get W. and set W=1/2 mv^2 ??
 
Physics news on Phys.org
1a) F = ma gives you the acceleration, use it to find v(t).
1b) With 1a) you can get an expression for the work performed by the force on the object. Relate the work to the power and express p(t).
1c) Use 1b).

2a) You can express the cars kinetic energy at 100 km/h. This energy has been received linearly in time.
2b) You know the kinetic energy given after 4 s from 2a), relate it to velocity.
 
2b. How can I know kinetic energy at 4s ? does the kinetic energy stay the same as in part a ??
 
nns91 said:
2b. How can I know kinetic energy at 4s ? does the kinetic energy stay the same as in part a ??
Well, it differs in time, but it is given linearly according to the problem description, starting at 0 going up to the maximum value after 8 s. From 2a) you can express energy given per time unit which should give you energy given after 4 s.
 
Can I just calculate the acceleration and find velocity from there ?
 
Can I just calculate the acceleration and find velocity from there ?
 

Thread 'Errors and significant figures'

I multiplied the values first without the error limit. Got 19.38. rounded it off to 2 significant figures since the given data has 2 significant figures. So = 19. For error I used the above formula. It comes out about 1.48. Now my question is. Should I write the answer as 19±1.5 (rounding 1.48 to 2 significant figures) OR should I write it as 19±1. So in short, should the error have same number of significant figures as the mean value or should it have the same number of decimal places as...
View full post »
Thread 'A cylinder connected to a hanging mass'

Thread 'A cylinder connected to a hanging mass'

Let's declare that for the cylinder, mass = M = 10 kg Radius = R = 4 m For the wall and the floor, Friction coeff = ##\mu## = 0.5 For the hanging mass, mass = m = 11 kg First, we divide the force according to their respective plane (x and y thing, correct me if I'm wrong) and according to which, cylinder or the hanging mass, they're working on. Force on the hanging mass $$mg - T = ma$$ Force(Cylinder) on y $$N_f + f_w - Mg = 0$$ Force(Cylinder) on x $$T + f_f - N_w = Ma$$ There's also...
View full post »

Similar threads

When is power constant in this scenario?
Replies
25
Views
2K
What is the power input of a motor pulling up an elevator?
Replies
3
Views
3K
Resistance force changing the velocity of an object
Replies
8
Views
1K
Work Kinetic energy using variable force
Replies
8
Views
2K
What Is the Average Power of Bullets Bouncing Off Superman?
Replies
26
Views
3K
Is potential energy defined only for internal conservative forces?
Replies
15
Views
1K
Maximizing Range/Time in Air of an Airplane: Solving with Calculus
Replies
4
Views
2K
Ratio of Power between Two Cars
Replies
14
Views
2K
How is Work and Power Calculated in These Scenarios?
Replies
1
Views
2K
Finding Frictional Force and Power Using Work and Energy
Replies
4
Views
3K

Hot Threads

Recent Insights

Back
Top