30N force is exerted and the trolley moves a distance of 5m in the direction of force, the work done is…….
a) 6J
b) 25J
c) 150J
d) 0.17N
Explanation: W = F × d so, W=30 N × 5m = 150J
If the speed of a car decreases by half, the kinetic energy change by factor
a) 4
b) 2
c) 1/2
d) 1/4
An object of mass 10 kg is lifted vertically through a height of 5m.
the gravitational potential energy gained by the object is……….
a) 0.5J
b) 2J
c) 50J
d) 490J
Explanation: P.E=mgh So,
P.E=10kg × 9.8m/s2 × 5m = 490J
If a petrol engine does 20J of useful work for every 100J of energy supplied to it, then its efficiency is……….
a) 80%
b) 60%
c) 40%
d) 20%
Hira weighing 500N takes 90s to reach the top of hill 18m high, her
average muscle power is
a) 2500W
b) 100W
c) 32.8W
d) 3.24W
Explanation: P=W/t, P=wxh/t, P= 500x18/90 =100W
A machine is able to lift 200N of concrete slab vertically up to a height of 30m above the ground in 50s. The average power of machine is………………
a) 1.33W
b) 60W
c) 120W
d) 6000W
Explanation:
P=W/t , P=w × h/t, P=200x30/50=120W
