JAMB Physics Past Questions & Answers - Page 418

2,086.

A 100kg box is pushed along a road with force of 500N. If the box moves with a uniform velocity, the coefficient of friction between the box and the road is

0.4

1.0

0.8

0.5

View answer & explanation

Correct answer is D

Coefficient of friction μ = ^F/_R = ^F/_mg = 500/1000 = 0.5
∴ μ = 0.5

2,087.

In a hydraulic press , a force of 40N is applied on the effort piston of area 0.4m². If the force exerted on the load piston is 400N, the area of the large piston is

4m²

8m²

2m²

1m²

View answer & explanation

Correct answer is A

Pressure developed in the effort piston = ^F/_a
∴^F/_a = ⁴⁰/_0.4 = ⁴⁰⁰/₄ = 100Nm²
this pressure is transmitted to the larger piston of area A; => P = ^F/_A
∴ 100 = ⁴⁰⁰/_A
=> A = ⁴⁰⁰/₁₀₀ = 4m²

2,088.

I. Jet propelled aircraft
II. Rocket propulsion
III. The recoil of a gun
IV. A person walking
Which of the above is based on Newton's third law of motion

I and II only

I, II, III, and IV only

I and III only

I, II and III only

View answer & explanation

Correct answer is B

No explanation has been provided for this answer.

2,089.

A machine whose efficiency is 60% has a velocity ratio of 5. If a force of 500N is applied to lift a load P, what is the magnitude of P?

1500N

500N

4166N

750N

View answer & explanation

Correct answer is A

efficiency = (M.A / V.R) x 100/1 => ⁶⁰/₁₀₀ = ^M.A/₅
∴M.A = (60 X 5) / 100 = 3
But M.A = Load/Effort; => 3 = Load/500
∴Load = 500 x 3
= 1500N

2,090.

A body of mass 4kg is acted on by a constant force of 12N for 3 seconds. The kinetic energy gained by the body at the end of the time is

144J

162J

81J

72J

View answer & explanation

Correct answer is B

K.E = ¹/₂MV²
Force, F = ma => a = ^F/_m = ¹²/₄ = 3ms^-2
But a = (V-U) / t => V = u + at
If the initial velocity U = 0, then V = at = 3 x 3 = 9ms^-2
∴ K.E, = ¹/₂ms^-2
¹/₂ 4 x 9 x 9 = 162J