A 500kg car has friction-free wheels. Two people begin pushing it on a level sur

ID: 2107516 • Letter: A

Question

A 500kg car has friction-free wheels. Two people begin pushing it on a level surface at t=0. The maximum

force each can deliver is 100N. At t=2s, one pusher is exhausted and quits. At t=4s, the second pusher is also

exhausted, and quits.

1) How fast is the car going at t=2s?

2) How fast is the car going at t=4s?

3) How far has the car moved from the starting point at t=2s?

4) How much work did the first pusher do before quitting at t=2s?

5) Just before the second pusher quits at t=4s, what power is the pusher delivering to the car?

The car and pushers are now going uphill at 5 degree's

1) How fast is the car going at t=2s?

The car going uphill now has a static coefficient of friction of .01 and a kinetic coefficient of friction .006:

1) Can the pushers overcome the static friction and move the car uphill?

2) How fast will the car be going at t=2s?

a)upto 2 sec F=200N. So a=0.4m/s^2

So v=0.4*2=0.8m/s

b)at t=4sec

v=0.8+0.2*2=1.2m/s

c)at t=2 sec

s=1/2at^2=0.5*0.4*4=8m

d)W(by one pusher)=100*8=800J

e)P=Fv=100*1.2=120W

a)max. static friction=0.01*5000cos(5)=49.81N<F So pushers can overcome static friction.

So 200-5000sin(5 deg)-0.006*5000cos(5 deg)=500a

so a=-ve. So car cannot move.

so at t=2 sec v=0.

assuming it is already uphill, then downward acc can be found.

5000sin(5 deg)-200-0.006*5000cos(5 deg)=500a

a=0.412m/s^2

so v=at=0.814m/s down the slope

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.