Question

A car weighing 1400kg is moving at a speed of 54km/h up a hill when the motor stops.If it is just able to reach the destination which is at height of 10 m above the point, calculate the work done against friction.

Answer 1

i guess u can use work energy therom


let work done by friction be x

ΔK.E=mgh+x

x= -1/2mv²-mgh
we know v , we know m, put g =10 u ll get ans

if i m not wrong ans is :307500
check calculation tho i might be wrong

Answer 2

Explanation:

Here given in the question :-

Car Mass m = 1400 kg .

h = 10 m

Moving at Initial speed v= 54 km/h = (54000/3600) m/s = 15 m/sec.

Now Initial Kinetic Energy of the car ,

= 1/2 mv²

= 1/2 (1400 x 15²)

= 315000/2

= 157500 J.

Here final velocity and Final Kinetic energy both are Zero.

Now change in Kinetic Energy  

= Final - Initial

= 0 - 157500

= -157500 J.

So change in Kinetic energy is also equal to W.D by all force.

Thus work done by gravity,

= mgh

= 1400 x 9.8 (-10)

= 1400 x -98

= -137200 .

Here, change in Kinetic energy = Work done by the friction + Work done by the gravity.

-157500 = Work done by friction + (- 137200)

Work done by the friction = -157500 +137200

=  -20,300

Hence, the work done against the friction =  20300 J